Using Debian 10.3 and Sendmail Version 8.15.2, mail being sent with relay=[127.0.0.1] results in stat=Deferred: Name server: [127.0.0.1]: host name lookup failure. This occurs only 3% of all localhost relays.
What would cause this?
Example mail.log results
Feb 14 11:20:29 themail sendmail[15759]: 31EGK5RK015759: Authentication-Warning: themail.themailserver.net: www-data set sender to "Dorothy Gale" <[email protected]> using -f
Feb 14 11:20:29 themail sendmail[15759]: 31EGK5RK015759: from="Dorothy Gale" <[email protected]>, size=2223, class=0, nrcpts=3, msgid=<[email protected]>, relay=www-data@localhost
Feb 14 11:20:31 themail sendmail[15759]: 31EGK5RK015759: to=<[email protected]>, ctladdr="Dorothy Gale" <[email protected]> (33/33), delay=00:00:26, xdelay=00:00:02, mailer=relay, pri=92223, relay=[127.0.0.1] [127.0.0.1], dsn=4.0.0, stat=Deferred: Name server: [127.0.0.1]: host name lookup failure
Feb 14 11:40:02 themail sm-msp-queue[30837]: 31EGK5RK015759: to="Tin Man" <[email protected]>,"Toe Toe" <[email protected]>,<[email protected]>, delay=00:19:57, xdelay=00:00:00, mailer=relay, pri=182223, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (31EGe1nu030852 Message accepted for delivery)
Feb 14 11:40:02 themail sm-mta[30852]: 31EGe1nu030852: from=<[email protected]>, size=2566, class=0, nrcpts=3, msgid=<[email protected]>, proto=ESMTP, daemon=MTA, relay=localhost [127.0.0.1]
Feb 14 11:40:02 themail opendkim[12211]: 31EGe1nu030852: DKIM-Signature field added (s=default, d=TheRecipiantDoamin.com)
Feb 14 11:40:02 themail sm-mta[30852]: 31EGe1nu030852: Milter insert (1): header: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple;\n\td=TheRecipiantDoamin.com; s=default; t=1676392802;\n\tbh=HDWWaKIqjIoy41TxrIV4xT1SeTcVPoqqqtbILYBejfQ=;\n\th=Date:From:To:CC:Subject;\n\tb=XWTcgXsIwtaJy+RNdHEDMh9pQZZ7fGyR9jvrCd9GWmuOXW4PsGFpNrmy+Nhs/vAu5\n\t TWIZSqXvrP8rLznaS/6zscwkcBOYJ1Pe3RH23qG7SL/z3DMJ4M8ds0xFUeew+C6bCD\n\t cjRvdmv9JnPTNtFLyxP4OxcHz2rE9TUOXURWUybw=
Feb 14 11:40:03 themail sm-mta[30871]: 31EGe1nu030852: to=|/export/home/projdata/TheRecipiantDoamin.com/mail_receiver/symbolic_links/tinman, ctladdr=<[email protected]> (8/0), delay=00:00:01, xdelay=00:00:01, mailer=prog, pri=93122, dsn=2.0.0, stat=Sent
Feb 14 11:40:03 themail sm-mta[30871]: 31EGe1nu030852: to=|/export/home/projdata/TheRecipiantDoamin.com/mail_receiver/symbolic_links/toetoe, ctladdr=<[email protected]> (8/0), delay=00:00:01, xdelay=00:00:00, mailer=prog, pri=93122, dsn=2.0.0, stat=Sent
Feb 14 11:40:04 themail sm-mta[30871]: 31EGe1nu030852: to=|/export/home/projdata/TheRecipiantDoamin.com/mail_receiver/symbolic_links/oz, ctladdr=<[email protected]> (8/0), delay=00:00:02, xdelay=00:00:01, mailer=prog, pri=93122, dsn=2.0.0, stat=Sent
cat /etc/hosts shows first line correctly as 127.0.0.1 localhost
cat /etc/resolv.conf shows
search themailserver.net
nameserver 8.8.8.8
