Hi, mailops
Recently I experienced a very "interesting" case which gave my personal
email server "poor" "sender score" due to high rate of emails sent from
my server to non-existent users.
It _couldn't_ be right, as the server is used only by myself and some
very few family members, and there is no activity which should have
triggered that score.
I think I figured out what it was. A user sent an email to another
family member, but using contact's old email domain which used to be
hosted by Fastmail, but where no such user would exist anymore (I don't
know if domain still exists as a domain at Fastmail, but clearly MX
point to them).
I'd guess a 5xx response would be appropriate -- at least on port 25,
but Fastmail sent 451, and made my Exim try -- and keep re-trying -- all
IP addresses of all their MX. I have very conservative retry rules, so
emails would be kept in the queue for a month...
I _guess_ that Fastmail is using sender score, because sender score
graphs started at the date of that one particular email was sent. So
every try must have been giving me "bad" score.
And I wouldn't even have discovered that if not OpenSMTPD misc@ lits
rejected my email, and today would accept it, but add a sender-score
header, which made me start digging...
Senders to Fastmail beware, and maybe consider treating their 4xx errors
as permanent.
Logs below:
Oct 7 08:45:03 chroot exim[7614]: 1qlZA1-00000000L8M-1jBn
H=in1-smtp.messagingengine.com [103.168.172.220]: SMTP error from remote
mail server after RCPT TO:<...>: 451 4.7.1 <...>: Relay access denied
Oct 7 08:45:06 chroot exim[7614]: 1qlZA1-00000000L8M-1jBn
H=in1-smtp.messagingengine.com [103.168.172.218]: SMTP error from remote
mail server after RCPT TO:<...>: 451 4.7.1 <...>: Relay access denied
Oct 7 08:45:08 chroot exim[7614]: 1qlZA1-00000000L8M-1jBn
H=in1-smtp.messagingengine.com [103.168.172.216]: SMTP error from remote
mail server after RCPT TO:<...>: 451 4.7.1 <...>: Relay access denied
Oct 7 08:45:10 chroot exim[7614]: 1qlZA1-00000000L8M-1jBn
H=in1-smtp.messagingengine.com [103.168.172.219]: SMTP error from remote
mail server after RCPT TO:<...>: 451 4.7.1 <...>: Relay access denied
Oct 7 08:45:13 chroot exim[7614]: 1qlZA1-00000000L8M-1jBn
H=in1-smtp.messagingengine.com [103.168.172.217]: SMTP error from remote
mail server after RCPT TO:<...>: 451 4.7.1 <...>: Relay access denied
Oct 7 08:45:16 chroot exim[7614]: 1qlZA1-00000000L8M-1jBn
H=in2-smtp.messagingengine.com [64.147.123.52]: SMTP error from remote
mail server after RCPT TO:<...>: 451 4.7.1 <...>: Relay access denied
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