First of all, thank you to the whole community of developers and testers for this project, which I appreciate very much.
[In the rest of the post, my domain name will be replaced by domain.tld, the IP of the main MX server with 220.127.116.11 and that of the MX 2 by 18.104.22.168].
I installed in early June 2020 a Mailcow instance on a server with a dedicated IPv4, and a correctly defined PTR record on it.
Then, following this guide, I configured a 2nd server as a secondary MX for my domain, so that it keeps cached emails when the main server encounters problems. However, I didn’t configure
relay_recipients on this second server, preferring to let Mailcow take care of this part.
I had not, since these two installations, made any update on these two servers (yes it’s bad).
I updated Mailcow yesterday, and, since then, the secondary server seems not to be able to relay incoming mails anymore: they remain in queue, with the status
mail for domain.tld loops back to myself.
From what I understood, this error could be caused by an identical
hostname on both servers; however this is not the case, the Mailcow server having as name
mail.domain.tld, and the MX 2,
Translated with www.DeepL.com/Translator (free version)
State of the queue on MX 2 (obtained with
-Queue ID- --Size-- ----Arrival Time---- -Sender/Recipient-------
1A0AD23F08B 3174 Mon Dec 7 11:39:57 email@example.com
(mail for domain.tld loops back to myself)
mail.domain.tld when running
postqueue -i 1A0AD23F08B on MX 2:
postfix-mailcow_1 | Dec 7 15:10:57 mail postfix/postscreen: CONNECT from [22.214.171.124]:45902 to [172.22.1.11]:25
php-fpm-mailcow_1 | fd4d:6169:6c63:6f77::d - 07/Dec/2020:15:10:57 +0100 "GET /forwardinghosts.php" 200
nginx-mailcow_1 | fd4d:6169:6c63:6f77::f - - [07/Dec/2020:15:10:57 +0100] "GET /forwardinghosts.php?host=126.96.36.199 HTTP/1.1" 200 20 "-" "curl/7.64.0"
postfix-mailcow_1 | Dec 7 15:10:57 mail whitelist_forwardinghosts: Look up 188.8.131.52 on whitelist, result 200 PERMIT
postfix-mailcow_1 | Dec 7 15:10:57 mail postfix/postscreen: WHITELISTED [184.108.40.206]:45902
postfix-mailcow_1 | Dec 7 15:10:57 mail postfix/smtpd: connect from mx2.domain.tld[220.127.116.11]
postfix-mailcow_1 | Dec 7 15:10:58 mail postfix/smtpd: Anonymous TLS connection established from mx2.domain.tld[18.104.22.168]: TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256
postfix-mailcow_1 | Dec 7 15:10:58 mail postfix/smtpd: disconnect from mx2.domain.tld[22.214.171.124] ehlo=1 starttls=1 quit=1 commands=3
main.cf of both MX1 (Mailcow server) and MX2 (SImple postfix backup server), if needed.
Thanks in advance for your precious help !!