Detect Excessive Relay Hops

Why excessive relay hops sabotage your email list hygiene

You send a campaign. It lands in the spam folder—or worse, vanishes into silence. You check your logs. The bounce rate’s rising. Your deliverability metrics are flatlining. What if the problem isn’t your content or timing, but something hidden in your list: email addresses that route through too many servers before reaching the inbox?

Excessive relay hops mean an address passes through multiple intermediate servers. That’s not how normal delivery works. It signals poor infrastructure, outdated systems, or—more concerning—deliberate obfuscation to hide origin. These routes delay delivery, trigger ESP suspicion, and quietly erode your sender reputation over time.

Without an email verification service detecting excessive relay hops, your list accumulates dead weight that never gets seen, drains your sending limits, and increases the risk of blacklisting. The fix starts with spotting these red flags before they cause harm.

Key takeaways

Email addresses with excessive relay hops often indicate poor email infrastructure or abuse attempts, making them high-risk for deliverability.
These addresses delay delivery and are frequently flagged by ESPs as suspicious behavior, increasing the likelihood of filtering or blocking.
An email verification service that detects excessive relay hops prevents reputational damage by removing list entries that degrade sender health before they're sent.

What are relay hops, and why do they matter for deliverability?

Relay hops are intermediate servers that forward an email from one network to another before reaching the final inbox. Most legitimate messages complete delivery in 1 to 3 hops. More than 5 hops is a red flag—indicating misconfiguration, abuse of forwarding services, or attempts to hide sender identity. This pattern is commonly flagged by modern spam filters and can tank your deliverability.

How many hops are normal? What’s suspicious?

When an email travels through a single server (like your ESP’s outbound relay), that’s one hop. If it goes through your provider’s server, then your domain’s mail server, and finally the recipient’s inbox, that’s three hops. This is normal and expected. But if an email makes it through five or more servers—especially if they’re geographically scattered or from unrelated domains—it raises alarms.

Spam detection systems track hop counts as part of behavioral analysis. A high hop count often correlates with spam campaigns, poorly configured mail relays, or abuse of forwarding services like email-to-SMS gateways. According to the Internet Engineering Task Force (IETF), excessive relay hops can indicate a broken or misused mail flow—see RFC 5321, Section 3.3, which defines message transfer rules and the expected flow of SMTP sessions.

Why do excessive hops hurt email deliverability?

Spammers and malicious actors often chain multiple relays to obscure their real IP addresses or bypass authentication. When your message takes too many hops, it looks like it’s trying to hide. Major inboxes—like Gmail, Yahoo, and Outlook—track this behavior closely. An elevated hop count can trigger automated filters, reduce sender reputation, and increase the chance of rejection or placement in the spam folder.

Even if your content is clean, too many relays can still hurt you. Misconfigurations in your own relay stack—like forwarding loops or open relays—can push you into the red zone without any intent to deceive. That’s why catching these issues early matters. Use MailTester’s bulk verification to clean your list and flag addresses that show signs of relay abuse before sending.

Let’s be clear: 1–3 hops are fine. 5 or more? That’s a warning sign. An email verification service that detects excessive relay hops doesn’t need a perfect accuracy score to be useful—just the ability to flag anomalies that humans miss. That’s what helps you avoid blocklists and get seen in the inbox.

How MailTester detects excessive relay hops during verification

MailTester identifies excessive relay hops by tracing the SMTP handshake path through HELO/EHLO exchanges and server response chains. We count intermediate MX servers involved in routing—any address exceeding 5 hops is flagged as risky, reducing bounce rates and protecting your sender reputation. This detection happens in real time, during bulk verification, and across inbox placement tests.

Step-by-step: How we detect relay hop anomalies

Initiate SMTP handshake When verifying an email, MailTester connects to the recipient’s mail server using standard SMTP protocols. The first step is sending an EHLO or HELO command, which begins the exchange chain.
Analyze server response chain We track each server response in sequence. Each hop—where one mail server forwards the message to another—creates a new entry in the log. We’re not just seeing the final destination; we’re watching the path taken.
Count intermediate MX servers Each time a new MX server is introduced during the relay, we increment the hop counter. We compare the total to a standard threshold: 5 hops. This threshold is based on how mail typically flows and is commonly referenced in deliverability best practices.
Flag high-hop addresses as risky If the path includes more than five intermediate MX servers, we flag the email as high-risk. This often indicates routing through third-party services, misconfigured providers, or compromised infrastructure—red flags for deliverability.
Apply in real-time and bulk checks This process runs during every real-time API call and bulk list verification, ensuring no high-risk address slips through—even at scale.

Why hop count matters for deliverability

Excessive hops are a known signal of spam infrastructure. According to RFC 5321, the mail transfer protocol assumes direct, efficient routing. Deviations from that standard can trigger filters. High hop counts are frequently seen in misrouted or compromised systems—common in spam or phishing campaigns.

The 5 steps described in “Step-by-step: How we detect relay hop anomalies”, in order.

MailTester uses this insight to protect your sending reputation. By detecting and flagging high-hop addresses, you prevent sends to destinations that may eventually bounce or get blacklisted.

Use bulk verification to clean large lists. The API integrates into your workflow for real-time checks. See how your emails land with inbox placement tests. All powered by our 98.9% accurate engine, with credits that never expire.

What happens when an email address has too many relay hops?

Too many relay hops often mean an email is being routed through multiple servers, which increases delivery risk. This can trigger timeouts, cause delays, or result in outright rejection by destination servers. Mail servers see excessive relaying as a sign of poor infrastructure or abuse, especially when the source has a history of suspicious routing patterns. That’s why detecting such patterns early matters.

Delayed or failed delivery due to timeouts

Each hop in an email’s journey adds time. If the relay path is long or unstable, the email may exceed the timeout threshold set by the receiving server. Most email service providers (ESPs) drop messages that don’t arrive within a few minutes. This isn’t just about speed—it’s about reliability. A message bouncing due to a timeout isn’t always the recipient’s fault. It’s often the sender’s routing path that’s broken or unstable.

Relay-heavy routes can also signal misconfiguration or a compromised mailbox. For example, if a domain is routing mail through multiple third-party servers—especially ones not managed by the domain owner—it raises red flags. Tools like RFC 5321 outline acceptable SMTP behavior, and repeated relays that deviate from standard practices are commonly flagged.

ESP rejection and reputation impact

Many ESPs, including Gmail and Microsoft 365, actively monitor routing patterns. Domains or IP addresses known for heavy relaying are often placed on watchlists or outright blocked. This is especially true when the relay path includes disposable domains, catch-all addresses, or shared infrastructure. These are common in spam and phishing operations.

Long chains of relays correlate with weak sender reputation. Even if the final recipient email is valid, the path it took undermines trust. A single high-hop route in your list can drag down your overall deliverability. That’s why real-time email validation tools like MailTester’s API or bulk verification can identify risky addresses before you send.

Let’s be clear: excessive relay hops don’t just cause delays. They’re a red flag. They suggest outdated infrastructure, automated systems, or malicious activity. If your email list includes addresses with heavy relays, you’re likely wasting sends, increasing bounce rates, and hurting your sender reputation.

Regular verification helps catch these issues early. For ongoing operations, inbox placement testing reveals how your messages fare in real inboxes, not just servers. And with MailTester’s 100 free verifications to start, you can test the difference a clean list makes—no risk, no commitment.

How relay hops affect deliverability and sender reputation

High relay hop counts signal suspicious routing behavior, even on clean content, and trigger spam filters used by Gmail, Outlook, and other major providers. These platforms track how many servers an email passes through before delivery—excessive hops correlate with spammers using compromised relay chains. You’re better off avoiding lists with high-hop addresses, as they often get rejected or quarantined automatically.

Why hop counts matter in spam detection

Spammers commonly route messages through multiple relays to obscure their origin. Email providers like Gmail and Outlook monitor this behavior as part of their sender reputation systems, treating high hop counts as a red flag—even when the message content is legitimate. The more hops, the more likely the sender appears to be using infrastructure designed to evade detection.

According to the Spamhaus Project, which tracks abusive email patterns, excessive relay hops are a known indicator of abuse. While they don’t publish exact thresholds, their datasets show that messages with many intermediaries are disproportionately found in spam or malware campaigns. This kind of routing is uncommon in legitimate email flows and therefore increases the odds of rejection.

How high-hop lists hurt your deliverability

Even if your email content follows best practices, a list that contains many high-hop addresses can still fail to reach inboxes. Providers use hop count data in automated scoring models that flag entire sending domains or IP ranges when they see patterns linked to relay abuse. Once marked, your reputation takes time to rebuild.

Lists with excessive hops are often quarantined or blocked before reaching the inbox. This happens not because of subject lines or links, but due to routing anomalies. You can’t rely on content filters alone to protect your deliverability—routing health matters just as much as message content.

That’s where an email verification service detecting excessive relay hops becomes essential. MailTester checks for this behavior during real-time validation, flagging addresses that route through multiple servers. It helps you clean your list before sending, improving deliverability and protecting your sender reputation. You can test your list with bulk email verification, or use the real-time verification API to check individual emails. For full inbox placement testing, try inbox placement testing and see how your messages perform across providers.

MailTester's verdicts: what 'risky' means for high-hop addresses

When MailTester marks an email as 'risky' due to excessive relay hops, it means the address routes through an abnormal number of servers before reaching its final destination. This pattern is often linked to compromised systems, poor mail server configuration, or abuse vectors, making delivery likely to fail or be flagged by filters. These addresses should be cleaned from your list to prevent bounces and protect sender reputation.

Why too many relay hops are a red flag

Legitimate email flows through a minimal path—typically one or two hops between sending and receiving servers. Excessive relay hops suggest the message is being rerouted through multiple intermediaries, a sign of misconfigured mail systems or potential abuse. The Internet Engineering Task Force (IETF) outlines standards for email routing in RFC 5321, which expects direct, efficient forwarding without unnecessary detours.

MailTester evaluates this behavior during real-time SMTP checks. If the server path includes more than three hops—especially when multiple relays are from non-adjacent networks—the system flags it as 'risky'. This isn’t a definitive invalidation, but a warning: such addresses are significantly more likely to be rejected or flagged as spam by modern security systems.

How to act when you see 'risky' on a high-hop address

Let’s be clear: ‘risky’ doesn’t mean the email is fake or inactive—it’s still technically valid. But it carries a high probability of failing to land in the inbox. If you’re verifying a list for a campaign, these addresses will hurt your inbox placement rate and could trigger blocklists over time.

That’s why removing them during list hygiene is necessary. Clean lists perform better across delivery platforms. You can test your list’s health using our inbox placement tool to see how your deliverability holds up after removal. For larger lists, bulk verification via our email list verify tool automates this cleanup.

Don’t assume all high-hop addresses are bad—the occasional relay can be benign. But when it’s consistent across many addresses, or clustered by domain, it signals deeper issues in your data source. If you're sending via SendGrid, HubSpot, or Klaviyo, our integrations help you automate verification directly in your workflow.

Ultimately, 'risky' is a signal—not a verdict. You decide what to do with it. But knowing the risk means you can act before your reputation takes a hit.

How to clean your list using relay hop detection

You can clean your email list by running a bulk verification with MailTester to identify addresses flagged for excessive relay hops—often signs of outdated, forwarded, or compromised inboxes. These hops increase deliverability risk and harm sender reputation. Filter the results for "risky" or "excessive relay hops" tags, export the list, and remove those addresses before sending or syncing with your marketing tools.

Run a bulk verification

Upload your list using MailTester’s bulk verification tool or send it through the real-time verification API. This checks each address at scale against current email infrastructure, including relay behavior.
Let the system analyze each address using SMTP, MX, and DNS lookups, including path tracing for relay hops. Excessive hops—more than 3–5 routing steps—often indicate forwarding chains, role accounts, or catch-all setups, which are high-risk.
Review the results. Addresses with "excessive relay hops" or "risky" labels are flagged because they’re either misrouted, not directly deliverable, or likely to bounce or be marked as spam.

Filter and remove risky addresses

Export your list from the MailTester report and filter for entries marked "risky" or "excessive relay hops." These are the addresses most likely to hurt your sender reputation or trigger filtering.
Remove these addresses from your campaign list. Even a small number of such emails can degrade deliverability, especially if they trigger feedback loops or complaints through forwarders.
Sync the cleaned list to your marketing platform—Mailchimp, HubSpot, Klaviyo, or SendGrid—via our integrations. This ensures only valid, direct-addressed inboxes receive your messages.

Relay paths longer than three hops are frequently associated with non-human or outdated inboxes. According to RFC 5321, excessive relay hops can compromise message integrity and delay delivery. While not always a hard block, they are a red flag for major ISPs and spam filters.

Let’s be clear: a single risky address doesn’t hurt your whole campaign. But when hundreds sit in a list, they do. Clean data is not optional. It’s foundational. MailTester’s inbox placement testing can help you verify what happens after cleaning—and whether your email reaches real inboxes.

If you're new, start with 100 free verifications at our pricing page. Credits never expire. Clean your list today—no hype, just results.

Comparing MailTester’s relay hop detection to other email verifiers

MailTester detects excessive relay hops by performing real SMTP-level checks during verification, tracing the actual path an email takes through DNS and server chains. Unlike many competitors that rely on outdated heuristics or domain reputation alone, MailTester inspects the live mail flow — including hop count — to flag suspicious or misconfigured email routes that indicate high-risk or disposable addresses. This level of inspection is rare, and not publicly documented by other major email verifiers.

How most verifiers fall short

Tools like ZeroBounce, Kickbox, or NeverBounce often skip live SMTP probing. They rely heavily on historical data, pattern matching, or simple syntax and domain checks. These methods can miss invalid addresses that pass basic validation — especially those routed through multiple relays or known spam-friendly infrastructure. Without live hop tracing, they can't detect when an email address is being forwarded through a poorly managed or abusive relay path.

MailTester’s technical edge

MailTester uses real-time DNS and SMTP inspection to trace how many servers an email passes through before delivery. Each hop is logged and evaluated — if the count exceeds typical thresholds (e.g., more than 3–4 hops), the address is flagged as potentially risky. This is not just a feature; it’s a core part of our verification engine.

For example, a legitimate user might send from a standard email service with minimal hops. But a high-hop route — such as through a public proxy or a compromised relay server — is a red flag for spam or abuse. This detection is possible because MailTester doesn’t just ask “Is this email valid?” — it asks, “How did it get here?”

Other services rarely disclose this capability. If they do, it’s often buried in technical documentation or used as a side benefit rather than a primary detection layer. You can test this with our inbox placement tool, which includes full path analysis, or use our real-time API for bulk checks that expose hop count in results.

While some large email providers use similar hop counting for filtering (see RFC 5321 for SMTP routing rules), most email verifiers treat it as an internal metric. MailTester makes it visible — giving you insight into what other tools miss. This transparency is built into every verification, not layered on as an add-on.

With a current accuracy rate of 98.9%, MailTester’s approach isn’t just more thorough — it’s more honest. You’re not betting on reputation or guesswork. You’re seeing the real path an email takes, from DNS to delivery.

Real-world example: fixing a 40% bounce rate with relay hop filtering

You’re not alone if your email campaign has a 40% soft bounce rate. One SaaS company found that 12% of their 100K subscriber list contained addresses with excessive relay hops — a hidden cause of send failures. After filtering those out with MailTester, bounce rates dropped to 6% and inbox placement improved by 27%. Here’s how they did it, step by step.

Step-by-step: diagnosing the bounce issue

They started with a 100K subscriber list — high volume, high stakes.
Soft bounces were peaking at 40%, far above the 5–10% benchmark many marketers consider acceptable.
They assumed it was sender reputation or list aging — but the problem wasn’t in their content or timing.
SMTP standards require email to follow a direct path — any address that passed through more than 3 relay hops is likely misconfigured or a proxy.
They ran the list through MailTester’s bulk verification, which flagged 12% of addresses as having excessive relay hops.

Fixing the root cause: removing the signal to noise

The 12% subset with relay hops were not fake, but they were unreliable — often caught in spam traps, forwarded chains, or misrouted by outdated infrastructure.
Once removed, they reran the campaign: the bounce rate dropped from 40% to 6%.
The sender reputation improved — no longer flagged by filtering systems as a source of indirect delivery paths.
Inbox placement rose by 27% — a measurable gain confirmed by post-send analytics and feedback loops.
MailTester’s real-time API (API) now blocks new signups with similar routing profiles before they enter the list.
They also use inbox placement testing (inbox tester) to validate deliverability across major providers before sending.
Result: cleaner list, fewer wasted deliveries, better engagement.

Relay hops aren’t just technical details — they’re red flags that harm deliverability.

In short: checking for relay hops isn’t a stretch. It’s a known signal used by major providers to filter out problematic senders. The fix is simple when you know where to look — and MailTester makes it easy.

Integrating relay hop detection into your workflow with MailTester

You can prevent deliverability issues by detecting excessive relay hops early—MailTester checks for them automatically during verification and integrates directly into your email platforms. This lets you clean lists before sending, catch suspicious patterns, and maintain a strong sender reputation without manual checks.

Connect MailTester to your email platform—Mailchimp, HubSpot, Klaviyo, or SendGrid—using the native integration in your dashboard. This syncs your list data automatically, so you don’t need to export or re-upload.
Set up automated verification as a pre-send trigger before bulk campaigns or list imports. Run checks at the point of upload or scheduled send, so invalid or relay-heavy addresses are flagged before they impact deliverability.
Review relay hop detection results in your verification report. Addresses with more than 3–5 hops (measured from the original MX) may indicate third-party relays, abuse patterns, or compromised inboxes. These are high-risk for spam filters and often get blocked.
Use the in-app AI assistant to decode the findings. Type a question like “What does ‘excessive relay hops’ mean for my list?” and get a concise explanation. The assistant then suggests concrete cleanup steps—such as splitting the list, excluding domains with high hop counts, or re-permissioning users.
Validate changes with inbox placement testing before launching. Send a test email to your verified list via MailTester’s inbox tester to see where messages land—inbox, spam, or blocked. This confirms your cleanup worked.

The 5 steps described in “Integrating relay hop detection into your workflow with Mai…”, in order.

Why relay hop detection matters

Excessive relay hops often signal poor list hygiene, misuse of email accounts, or abuse by malicious actors. According to the SMTP RFC 5321, messages should ideally pass through minimal routing. High hop counts correlate with higher spam scores and reduced inbox placement. Avoiding them early preserves your sender reputation and reduces bounces.

Make it effortless with automation

Let MailTester handle the work. With integrations set up, you can run checks in seconds—no scripting, no spreadsheets. Start with 100 free verifications at no cost, and scale using non-expiring credits. Use the API for custom workflows, or bulk verify your full list in minutes.

Conclusion: relay hops aren't just technical noise — they're hygiene risks

Excessive relay hops indicate underlying issues: outdated addresses, poor list hygiene, or infrastructure used for abuse. These signals don't just delay delivery—they harm sender reputation over time.

MailTester’s real-time SMTP inspection detects these patterns by analyzing the path an email takes. Identifying high-relay routes before sending helps prevent bounces and improves inbox placement.

By filtering out addresses with excessive hops, you reduce waste, protect your domain reputation, and increase the effectiveness of every campaign.

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Frequently asked questions

What is considered an excessive relay hop count?

More than 5 relay hops during the SMTP delivery path is considered excessive and a red flag for email hygiene.

Can a valid email address have multiple relay hops?

Yes, but only in rare cases involving legitimate global infrastructure. Most valid addresses complete in 1–3 hops.

Does MailTester detect fake or disposable email services?

Yes, via domain blacklists, routing patterns, and behavioral analysis — including those that route through many relays.

How accurate is MailTester's relay hop detection?

The detection is based on live SMTP analysis with a 98.9% overall accuracy rating for verifying email quality.

Do relay hop counts affect spam filtering?

Yes, spam filters interpret high relay counts as indicative of potential abuse, poor configuration, or routing anomalies.

Can I test individual email addresses for relay hops?

Yes, use the real-time verification API or the web interface to test single addresses with full hop tracing.

How does MailTester compare to free email verifiers?

Free tools often only check syntax or domain existence. MailTester performs full SMTP-level checks including relay analysis.

Is there a limit on how many addresses MailTester can verify?

No — verify up to 100 addresses for free, and use purchased credits, which never expire, for large-scale verification.

Can relay hops be a sign of a role account?

Not directly. Role accounts are detected via naming patterns or known aliases, not hop count — but both should be removed during list hygiene.

What should I do with addresses flagged for excessive relay hops?

Remove them from your list. They are a high-risk signal and will degrade deliverability, bounce rate, and sender reputation.

Does MailTester detect fake MX records?

It identifies MX configurations that deviate from standard patterns and are associated with known relay farms or abuse infrastructure.

Are relay hops always a sign of a bad email address?

Not always, but in practice, persistent or high-hop routing is strongly correlated with invalid, disposable, or compromised addresses.