Frequently Asked Questions
- How does e-mail work?
- How does MailTester.com work?
- Does MailTester.com always work?
- Is e-mail guaranteed to either be delivered or bounced?
- Is it possible that I can send e-mail, but not receive anything (or the other way around)?
- Where does MailTester.com come from?
- Can I get the source code?
- Can MailTester.com check a whole list of e-mails?
- Can I call MailTester.com from my application or website via an API?
How does e-mail work?
When an e-mail is sent, the following actions are taken:
- The destination mail server is determined by asking the DNS-server which server is responsible for the domain. The domain is the part after the @-sign in the e-mail address.
- An SMTP connection is made to that mail server (or, if it's not available, to the next mail server that is responsible for the domain). This is where the e-mail gets transferred to the recipient's mailbox.
- The recipient will find the mail when checking the mailbox (e.g. using webmail or software using the POP3 or IMAP protocol).
How does MailTester.com work?
MailTester.com checks if the e-mail address is syntactically valid, looks up the SMTP server responsible for the e-mail address in DNS, and tries to establish an SMTP connection. It then tries to send several commands, almost as if an e-mail is going to be sent. When enough information is gathered, the connection is aborted and no actual e-mail is sent.
Does MailTester.com always work?
No, not always. Verifying e-mail is not possible a 100% of the time.
The valid syntax of the address and the domain (= the part after the @-sign) can always be verified.
However, the local part (= the part before the @-sign) may not be possible in some cases. A few examples:
- If the mail server containing the mailbox is behind another server, that server may not even have information about the validity of the e-mail address.
- Some mail servers accept any e-mail address for the domain(s) they are responsible for - even invalid addresses. This is known as a catch-all server.
- Anti-spam measures in mail servers may cause mail servers to take actions which make checking (temporarily) impossible (e.g. refusing connections).
Any mail verification service will run into these same challenges. Other solutions may flag the mail as valid, but MailTester.com will show the real status.
Is e-mail guaranteed to either be delivered or bounced?
No. There is no guarantee an e-mail is delivered, even if you didn't receive a bounce-mail.
There are several possible scenarios where you would not receive a bounce mail.
For example: when an SMTP server suddenly finds itself isolated from the Internet, it will not be able to send a bounce-mail.
Or maybe your address is not reachable so the bounce mail could not be delivered to you.
Is it possible that I can send e-mail, but not receive anything (or the other way around)?
Yes, sending and receiving are completely different things.
For sending you need to be able to contact the SMTP server.
For receiving you need to have access to your mailbox, usually via POP3 or IMAP. For mail to be able to arrive into your mailbox, your mailserver has to be registered in the DNS system, and it has to be reachable from the Internet.
Since sending and receiving are completely different actions, one can sometimes work while the other doesn't.
Where does MailTester.com come from?
A lot of people come to me asking if a certain e-mail address is having problems or why a certain e-mail address doesn't work. Usually the answer is in the bounce-mail, but often it is in such technical terms most people don't know what it means.
There are some routine tests I usually do to find out more about an e-mail address.
I decided to automate these tests, and make them available for everybody on this site.
Can I get the source code?
No, the source of MailTester.com is not available.
If you are looking for open source maybe these projects (from the same author as MailTester.com) may be interesting:
Free cross-platform library for C and C++ and command line application for sending e-mail with support for multiple attachments.
Free program for use in logon scripts in Microsoft Windows environments to generate Microsoft Outlook e-mail signatures based on templates and LDAP (Active Directory) data. This allows network administrators to set the same centrally managed Outlook signature layout for a large group of people.
Can MailTester.com check a whole list of e-mails?
MailTester.com offers a cloud solution that can check a list of e-mail address that you upload to it. Please click here to check it out.
Can I call MailTester.com from my application or website via an API?
Mailtester premium offers two easy-to-integrate and customizable APIs:
- Bulk email check API
- Real-time email check API.
Available for several programming languages:
For more details, please visit the API section.