tonline-ptr-rules

2 posts

Inbox placement by mailbox provider: Gmail, Outlook, Yahoo and spam filters

T-Online Blocks IPv6 Mail Servers — Use IPv4 Only in 2026

Fix T-Online email delivery issues caused by IPv6. Learn why T-Online rejects IPv6 mail and how to verify sender infrastructure with real-time validation.

Email authentication: SPF, DKIM, DMARC, BIMI and MTA-STS

T-Online PTR Record Must Resolve to Website with Impressum

Ensure your T-Online PTR record resolves to a website with Impressum to avoid email delivery issues in Germany. Test and verify with real-time tools.