I have to come back to this older thread of mine https://community.sophos.com/utm-firewall/f/mail-protection-smtp-pop3-antispam-and-antivirus/120948/outbound-mails-fail-with-greylisting---no-second-attempt because the problem is biting me again (or rather: still).
Situation summary (cf. above link): Outbound mail to a certain external domain fails without retry. They use greylisting (and so do we, but that is not the point here) and they reply with "451 4.7.1 Please try again later". As per RFC3463, both a 4xx basic status code and a 4.x.x extended status code indicate temproary failures and should thus make my UTM retry (even though section 3.8 of that RFC suggests that x.7.1 makes sense only in a permanent 5xx error)
Meanwhile, I found that exim had this behaviour (no retry when seeing a "451 4.7.1") already in 2013: https://lists.exim.org/lurker/message/20130305.141251.4c429c98.de.html or https://www.mail-archive.com/exim-users@exim.org/msg43004.html -- where there apparently was no solution
and in 2007 https://lists.exim.org/lurker/message/20070529.165025.0b32c5de.ja.html -- where the successful solution was to upgrade exim to version 4.67 (but we are already at 4.82)
I also wanted to try (as suggested by Balfson in the referenced tread)
/var/mdw/scripts/smtp stop
dropdb -U postgres smtp
createdb -U postgres smtp
/var/mdw/scripts/smtp start
However, even though the first line succeeds
::Stopping SMTP Proxy
[ ok ]
I cannot run the second line
dropdb: database removal failed: ERROR: database "smtp" is being accessed by other users
DETAIL: There are 7 other sessions using the database
The number 7 (supposedly caused by mails in progress?) does not go down if I try later. After several retries over more than a minute, I started smtp again. Another attempt half an hour later resulted in the same "7 other sessions", so I assume that this "7" is systematic.
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