Mail tester complains about our SMTP banner or EHLO name
On every SMTP connection your server announces EHLO/HELO with a hostname. That name must be a valid FQDN with forward + reverse DNS matching your public sending IP. A hostname like 'localhost' or one that doesn't PTR-match costs reputation at large receivers.
Try this first
- 1Test with telnet or nc to port 25 of your MTA and read the banner. Or test outgoing via mail-tester.com.
- 2EHLO name must match the PTR (reverse DNS) of your sending IP. If IP is 1.2.3.4 with PTR mail.yourdomain.com, EHLO is also mail.yourdomain.com.
- 3On hosted: ask your provider to set PTR to the correct hostname. ISPs default to an ISP PTR that has nothing to do with your domain.
- 4In your MTA (Postfix: myhostname, Exchange: send connector FQDN) set the correct hostname. No 'localhost.localdomain'.
- 5Verify with dig -x 1.2.3.4 (PTR) and dig a mail.yourdomain.com (forward). Both must point to the same name.
When to bring us in
If you send via an ESP or M365, EHLO is already correct, nothing for you to do. This only matters with self-hosted.
See also
- Our emails land in spam for some recipientsAlmost always an SPF, DKIM, or DMARC setting that is wrong or missing, or a sender name that mimics a well-known brand.
- Someone reports receiving phishing emails "from us"Read: spoofing. Someone is abusing your sender name, not necessarily your actual mailbox.
- An email bounces (NDR): delivery failedThe NDR text usually states the exact reason. Reading it is step one.
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