Background: I run my own mail server and use Mail Avenger for SPAM protection. Mail Avenger will try to validate the envelope sender [MAIL FROM:<...>] by trying to connect back to the sender's domain. If that fails, the email is likely SPAM and will be rejected.
In this case, Brewer's Friend is sending out email messages with a syntactically correct sender address, but with a domain for which there is no SMTP server listening despite valid MX records being present. I'm assuming that this is an error that you would like to correct.
See below for details.
Regards,
Lennart Lövstrand
Oct 7 15:31:44 vps2 : asmtpd: accepted connection from 198.2.181.164:55593 (fd 7)
Oct 7 15:31:59 vps2 : mail164.suw18.rsgsv.net (7) <== 220 mail.lovstrand.com ESMTP
Oct 7 15:31:59 vps2 : mail164.suw18.rsgsv.net (7) ==> EHLO mail164.suw18.rsgsv.net
Oct 7 15:31:59 vps2 : mail164.suw18.rsgsv.net (7) <== 250-mail.lovstrand.com
Oct 7 15:31:59 vps2 : mail164.suw18.rsgsv.net (7) <== 250-STARTTLS
Oct 7 15:31:59 vps2 : mail164.suw18.rsgsv.net (7) <== 250 PIPELINING
Oct 7 15:31:59 vps2 : mail164.suw18.rsgsv.net (7) ==> MAIL FROM:<bounce-mc.us12_49116713.389353-lennart.brewersfriend=lovstrand.com@mail164.suw18.rsgsv.net>
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) <== 250 ok
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) ==> RCPT TO:<lennart.brewersfriend@lovstrand.com>
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) <== 451-There is a problem with sender <bounce-mc.us12_49116713.389353-lennart.brewersfriend=lovstrand.com@mail164.suw18.rsgsv.net>.
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) <== 451-It is not possible to send bounce messages to that address.
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) <== 451 could not connect to server for mail164.suw18.rsgsv.net
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) ==> DATA
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) <== 503 must follow rcpt
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) ==> QUIT
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) <== 221 mail.lovstrand.com
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) === EOF
$ host mail164.suw18.rsgsv.net
mail164.suw18.rsgsv.net has address 198.2.181.164
mail164.suw18.rsgsv.net mail is handled by 10 mail.mail164.suw18.rsgsv.net.
$ telnet mail.mail164.suw18.rsgsv.net 25
Trying 198.2.181.164...
telnet: Unable to connect to remote host: Connection timed out
In this case, Brewer's Friend is sending out email messages with a syntactically correct sender address, but with a domain for which there is no SMTP server listening despite valid MX records being present. I'm assuming that this is an error that you would like to correct.
See below for details.
Regards,
Lennart Lövstrand
Oct 7 15:31:44 vps2 : asmtpd: accepted connection from 198.2.181.164:55593 (fd 7)
Oct 7 15:31:59 vps2 : mail164.suw18.rsgsv.net (7) <== 220 mail.lovstrand.com ESMTP
Oct 7 15:31:59 vps2 : mail164.suw18.rsgsv.net (7) ==> EHLO mail164.suw18.rsgsv.net
Oct 7 15:31:59 vps2 : mail164.suw18.rsgsv.net (7) <== 250-mail.lovstrand.com
Oct 7 15:31:59 vps2 : mail164.suw18.rsgsv.net (7) <== 250-STARTTLS
Oct 7 15:31:59 vps2 : mail164.suw18.rsgsv.net (7) <== 250 PIPELINING
Oct 7 15:31:59 vps2 : mail164.suw18.rsgsv.net (7) ==> MAIL FROM:<bounce-mc.us12_49116713.389353-lennart.brewersfriend=lovstrand.com@mail164.suw18.rsgsv.net>
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) <== 250 ok
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) ==> RCPT TO:<lennart.brewersfriend@lovstrand.com>
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) <== 451-There is a problem with sender <bounce-mc.us12_49116713.389353-lennart.brewersfriend=lovstrand.com@mail164.suw18.rsgsv.net>.
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) <== 451-It is not possible to send bounce messages to that address.
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) <== 451 could not connect to server for mail164.suw18.rsgsv.net
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) ==> DATA
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) <== 503 must follow rcpt
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) ==> QUIT
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) <== 221 mail.lovstrand.com
Oct 7 15:33:02 vps2 : mail164.suw18.rsgsv.net (7) === EOF
$ host mail164.suw18.rsgsv.net
mail164.suw18.rsgsv.net has address 198.2.181.164
mail164.suw18.rsgsv.net mail is handled by 10 mail.mail164.suw18.rsgsv.net.
$ telnet mail.mail164.suw18.rsgsv.net 25
Trying 198.2.181.164...
telnet: Unable to connect to remote host: Connection timed out
