Proxmox as backup MX, it reject email when primary server down

[EricL]

Hi everyone, I got the email rejected from Proxmox MG when the primary server was offlined.

[timestmp] postfix/qmgr[]: from=<double-bounce@mx2.domain.com>, size=264, nrcpt=1 (queue active)
[timestmp] postfix/smtp[]: to=<user@userdomain.com>, relay=none, delay=0.13, delays=0.01/0.07/0.06/0, dsn=4.4.1, status=undeliverable (connect to mail.domain.com [IP]:25: Connection refused)
[timestmp] postfix/qmgr[]: removed

[timestmp] postfix/smtpd[]: connect from m16.senderserver.com[IP]
[timestmp] postfix/smtpd[]: NOQUEUE: reject: RCPT from m16.senderserver.com[]: 450 4.1.1 <user@userdomain.com>: Recipient address rejected: unverified address: connect to mail.domain.com[IP]:25: Connection refused; from=<user@senderserver.com> to=<user@userdomain.com> proto=ESMTP helo=<m16.senderserver.com>
[timestmp] postfix/smtpd[]: disconnect from m16.senderserver.com[IP] ehlo=1 mail=1 rcpt=0/1 quit=1 commands=3/4

I have configured the Proxmox MG as a secondary MX as following:
1. MX record configured priority 10 for primary server (e.g. mail.domain.com) and priority 20 Proxmox MG (e.g. mx2.domain.com)
2. Configured Transports for delay domain (userdomain.com) to the primary server (mail.domain.com)
3. Reject Unknow Client set to No
4. Verify Receiver set to Yes(550)
5. Before Queue Filtering is turned OFF.
6. It works normal when primary server are online, Proxmox can check the existence of recipient on primary server, accept the email and put it in queue and forward to primary server.

Issue:
When primary server is offlined, Proxmox MG cannot check the validity of recipient email and return a 450 4.4.1 Recipient address rejected: unverified address error to the sender server

May I know what should I do so that Proxmox can accept mails when the primary server is offlined? Thank you

 

[Stoiko Ivanov]

May I know what should I do so that Proxmox can accept mails when the primary server is offlined? Thank you

the results from address verification are cached - PMG uses postfix functionality for the recipient verification:
https://www.postfix.org/ADDRESS_VERIFICATION_README.html
and
https://www.postfix.org/verify.8.html
show which parameters can be used to tweak the lifetime of the cache.

all mail addresses which have been accepted in the past address_verify_positive_expire_time should be accepted and queued by PMG

however the point here is that PMG responded with a temporary error to the sender (450) so the sender should retry it (many mail-systems do so for 5 days) - if at some later point the downstream server is reachable again the mail will be accepted and delivered. if the downstream server is unreachable for 5 days PMG would also drop the mail (and in some cases send a bounce to the original sender)

I hope this helps!