:date: 2019-12-11 ============================ Wednesday, December 11, 2019 ============================ Learning about mail servers =========================== The PTR record issue seems fixed, but ticket :ticket:`3339` is still open. There are at least two mailing list on LF having this problem. The people say that they have no problem receiving mails to their @hot.ee address from other senders. I want to understand what's happening. ``mx1.hot.ee[194.126.101.119]:25`` continues to say "Service currently unavailable (in reply to RCPT TO command))" when LF wants to deliver them 3 mails to recipients `@hot.ee`. And when LF tries again 5 minutes later, it even says "550 5.7.1 Connection timed out (in reply to end of DATA command))". I guess they are using postscreen. Quote from the `docs `_: "In a typical deployment, postscreen(8) handles the MX service on TCP port 25, while MUA clients submit mail via the submission service on TCP port 587 which requires client authentication. Alternatively, a site could set up a dedicated, non-postscreen, "port 25" server that provides submission service and client authentication, but no MX service." How can I test an SMTP relay server from outside? I mean a little program that sends an email and then reports how the server "behaves". On `wormly.com `__ there is a page that does exactly what I mean. When sending to luc@lino-framework.org I get a normal answer:: Resolving hostname... Connecting... Connection: opening to lino-framework.org:25, timeout=300, options=array ( ) Connection: opened SERVER -> CLIENT: 220 mail.lino-framework.org ESMTP Postfix (Debian/GNU) CLIENT -> SERVER: EHLO tools.wormly.com SERVER -> CLIENT: 250-mail.lino-framework.org 250-PIPELINING 250-SIZE 10240000 250-VRFY 250-ETRN 250-STARTTLS 250-AUTH PLAIN 250-AUTH=PLAIN 250-ENHANCEDSTATUSCODES 250-8BITMIME 250-DSN 250-SMTPUTF8 250 CHUNKING CLIENT -> SERVER: STARTTLS SERVER -> CLIENT: 220 2.0.0 Ready to start TLS CLIENT -> SERVER: EHLO tools.wormly.com SERVER -> CLIENT: 250-mail.lino-framework.org 250-PIPELINING 250-SIZE 10240000 250-VRFY 250-ETRN 250-AUTH PLAIN 250-AUTH=PLAIN 250-ENHANCEDSTATUSCODES 250-8BITMIME 250-DSN 250-SMTPUTF8 250 CHUNKING CLIENT -> SERVER: MAIL FROM: SERVER -> CLIENT: 250 2.1.0 Ok CLIENT -> SERVER: RCPT TO: SERVER -> CLIENT: 250 2.1.5 Ok CLIENT -> SERVER: DATA SERVER -> CLIENT: 354 End data with . CLIENT -> SERVER: Date: Wed, 11 Dec 2019 09:34:17 +0000 CLIENT -> SERVER: To: luc@lino-framework.org CLIENT -> SERVER: From: Wormly SMTP Test CLIENT -> SERVER: Subject: Wormly SMTP Test Message CLIENT -> SERVER: Message-ID: <1639293d056826af4d71d7d9cf551c96@blog.wormly.com> CLIENT -> SERVER: MIME-Version: 1.0 CLIENT -> SERVER: Content-Type: text/plain; charset=iso-8859-1 CLIENT -> SERVER: CLIENT -> SERVER: This message was sent using the Wormly SMTP testing tool by this user: CLIENT -> SERVER: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:71.0) Gecko/20100101 Firefox/71.0 CLIENT -> SERVER: 84.50.167.213 CLIENT -> SERVER: CLIENT -> SERVER: . SERVER -> CLIENT: 250 2.0.0 Ok: queued as AA3D27E54 CLIENT -> SERVER: QUIT SERVER -> CLIENT: 221 2.0.0 Bye Connection: closed Message completed successfully. But when sending to lucsaffre@hot.ee I get the following answer:: Resolving hostname... Connecting... Connection: opening to hot.ee:25, timeout=300, options=array ( ) SMTP ERROR: Failed to connect to server: Connection refused (111) 2019-12-11 09:35:16 SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting Message sending failed. But then. Testing LF on `mxtoolbox.com `__ told me "Reverse DNS is not a Valid Hostname". More precisely "Your Reverse DNS Record (PTR) is not a valid host name. According to email sending best practices, a PTR Record should be a valid host name. If the PTR Record is not a valid hostname, there is a likelihood that you will experience email delivery issues with anti-spam services."" Finally I have a way to reproduce the problem! Thanks, mxtoolbox :-) The problem disappeared on mxtoolbox when I changed the reverse DNS name for my IP address from ``lino-framework.org.`` to ``mail.lino-framework.org.`` While it works now on mxtoolbox, I am now getting the following answer from ``mx1.hot.ee`` :: Dec 11 12:48:23 vps-ssd-1-sbg1 postfix/smtp[9360]: 118557D24: to=, relay=mx1.hot.ee[194.126.101.119]:25, delay=6.4, delays=0.69/0.06/5.4/0.18, dsn=4.3.2, status=deferred (host mx1.hot.ee[194.126.101.119] said: 450 4.3.2 Service currently unavailable (in reply to RCPT TO command)) Maybe their postscreen has blacklisted my server? I asked Telia to verify.