I have a server running Postfix (3.1.0-3ubuntu0.3) that has been in production for a few months and is generally working well. However I've been struggling to resolve an issue where some legitimate servers cannot send inbound mail, where there appears to be an issue with the sending server's DNS.
Here is an example: Mar 5 23:25:47 enceladus postfix/postscreen[5155]: CONNECT from [104.37.111.105]:51876 to [x.x.x.x]:25 Mar 5 23:25:47 enceladus postfix/postscreen[5155]: PASS OLD [104.37.111.105]:51876 Mar 5 23:25:47 enceladus postfix/smtpd[5159]: warning: hostname 104-37-111-105.static.dbsintl.net does not resolve to address 104.37.111.105: Name or service not known Mar 5 23:25:47 enceladus postfix/smtpd[5159]: connect from unknown[104.37.111.105] Mar 5 23:25:47 enceladus postfix/smtpd[5159]: disconnect from unknown[104.37.111.105] ehlo=1 mail=0/1 quit=1 commands=2/3 Details on the sending host: dig 104-37-111-105.static.dbsintl.net ; <<>> DiG 9.10.3-P4-Ubuntu <<>> 104-37-111-105.static.dbsintl.net ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 53175 ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION: ;104-37-111-105.static.dbsintl.net. IN A ;; AUTHORITY SECTION: dbsintl.net. 60 IN SOA ns1.ral.hostedsolutions.com. hostmaster.hostedsolutions.com. 2013061720 10800 3600 604800 604800 ;; Query time: 19 msec ;; SERVER: 172.31.0.2#53(172.31.0.2) ;; WHEN: Tue Mar 06 17:54:38 UTC 2018 ;; MSG SIZE rcvd: 136 My smptd recipient restrictions from main.cf: smtpd_recipient_restrictions = check_policy_service unix:private/policy-spf, reject_unknown_recipient_domain, reject_unauth_pipelining, permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination I previously had included reject_unknown_client_hostname, but removing it seems to have no effect. That's about the only seemingly relevant thing I've found online, and I'm really at a loss as to how to proceed. Also interesting, when attempting to register for the Postfix forum, I never received the confirmation e-mail and had to use a backup account. I have seen this behavior once or twice before, where the remote server connects and then disconnects without appearing to do anything, but have no idea where to begin troubleshooting it: Mar 6 17:37:13 enceladus postfix/postscreen[12658]: CONNECT from [162.253.133.81]:53413 to [x.x.x.x]:25 Mar 6 17:37:19 enceladus postfix/postscreen[12658]: PASS NEW [162.253.133.81]:53413 Mar 6 17:37:19 enceladus postfix/smtpd[12668]: connect from n5.nabble.com[162.253.133.81] Mar 6 17:37:19 enceladus postfix/smtpd[12668]: disconnect from n5.nabble.com[162.253.133.81] ehlo=1 mail=0/1 rcpt=0/1 data=0/1 rset=0/1 quit=1 commands=2/6 Please let me know what additional information needed to dig deeper into these issues. Thank you! -- Sent from: http://postfix.1071664.n5.nabble.com/Postfix-Users-f2.html
