Hi, I have a postfix-3.4.10 system being used as a relay for a subdomain where most users are forwarding their mail through it instead of sending and receiving email on it directly using a ~/.forward file and procmail.
Users can send and receive mail using their desktop email client connected through imap/submission or a webmail client. The problem is issues like this: 825FD80D40EBC 8283 Fri Jul 31 15:00:21 u...@yahoo.com (host mta7.am0.yahoodns.net[98.136.96.74] said: 421 4.7.0 [TSS04] Messages from 66.104.111.99 temporarily deferred due to user complaints - 4.1 6.55.1; see https://help.yahoo.com/kb/postmaster/SLN3434.html (in reply to MAIL FROM command)) This mail server has an SPF record for itself, but no DKIM or DMARC. It also has a working reverse DNS. Mail is received by this system from two postfix relays protected with spamassassin and monitored closely. Yahoo recommends messages are DKIM signed, but we were concerned about the effect mailing lists and other emails would have being forwarded through the server. We're also using two transport filters to deliver mail: polite unix - - n - - smtp -o syslog_name=postfix-polite turtle unix - - n - - smtp -o syslog_name=postfix-turtle We're specifying domains like yahoo to go through the turtle transport: /yahoo\.com$/ turtle: /yahoo(\.[a-z]{2,3}){1,2}$/ turtle: Perhaps that practice has changed and DKIM and DMARC should be implemented on relays now? Can someone recommend a set of best practices for using postfix to relay mail to yahoo/gmail in this way?
