Hi, I'm using postfix as an smtp filter (antispam) which then forwards the messages to another mail server with user mailboxes.
This server has private IP addr. 10.0.0.1, and the mailbox server has private IP addr. 10.0.0.10. So, external e-mails are first received by this filter and then forwarded to the mailboxes. It has been working fine for years, but a few days ago some e-mails were not coming in anymore, and the logs on the filtering server show messages such as this one: postfix/smtp[13093]: A306E1240B1: to=<m...@mydomain.org>, relay=none, delay=0.06, delays=0.06/0/0/0, dsn=5.4.6, status=bounced (mail for 10.0.0.10 loops back to myself) I'm still trying to understand what that means exactly. # grep mydomain.org /etc/postfix/* /etc/postfix/main.cf:proxy_interfaces = mail1.mydomain.org mail2.mydomain.org /etc/postfix/main.cf:relay_domains = mydomain.org mydomain2.org /etc/postfix/relay_recipients:@mydomain.org x Binary file /etc/postfix/relay_recipients.db matches /etc/postfix/transport:mydomain.org smtp:[10.0.0.10] Binary file /etc/postfix/transport.db matches Host resolution on the postfix server: # host mail1.mydomain.org mail1.mydomain.org has address 10.0.0.2 # host mail2.mydomain.org mail2.mydomain.org has address 10.0.0.1 NB: mail1.mydomain.org (10.0.0.2) is another postfix antispam server in the private network, but that shouldn't matter here. # dig +nocookie -t MX mydomain.org ; <<>> DiG 9.11.1-P1 <<>> +nocookie -t MX mydomain.org ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 43328 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 4 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 1280 ;; QUESTION SECTION: ;mydomain.org. IN MX ;; ANSWER SECTION: mydomain.org. 3600 IN MX 100 mail2.mydomain.org. mydomain.org. 3600 IN MX 10 mail1.mydomain.org. ;; ADDITIONAL SECTION: mail2.mydomain.org. 3600 IN A 10.0.0.1 mail1.mydomain.org. 3600 IN A 10.0.0.2 ;; Query time: 0 msec ;; SERVER: 10.0.0.31#53(10.0.0.31) ;; WHEN: Wed Apr 15 09:56:15 CEST 2020 ;; MSG SIZE rcvd: 155 I don't know how postfix decides that the mail destined to the mailbox server (10.0.0.10) should loop back to itself. How can I debug this? What should I be looking for? Regards, Vieri
