Backup jobs mails in deferred status

May 23, 2023

For a few weeks we have stopped receiving the emails that scheduled backup tasks send when they finish their execution.
We only receive emails if we execute them manually. When they automatically execute the emails, they remain in the 'deferred' state and are not sent.

root@pve01:/var/log# grep deferred maillog |head -n1
Feb 11 23:01:38 postfix/smtp[6152]: 167BD4C220B: to=<>, relay=none, delay=32, delays=0/0.02/32/0, dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for type=AAAA: Host not found, try again)

Thanks for your help
Host or domain name not found. Name service error for type=AAAA: Host not found, try again
The server is trying to resolve the domain to IPv6 (AAAA record) when sending the mail, which fails.

And it indeed seems like does not provide any AAAA record when checking with a DNS utility like dig (dig +short AAAA) or drill (drill -Q AAAA

But, do you even need to use IPv6 here? Else you might adapt the postfix config to make it use either IPv4 only, or at least try both (which isn't the default, it stops if the first fails). To do that edit /etc/postfix/, change (or add) the following line to either
inet_protocols = ipv4
for IPv4 only, or change the preference if you want that this host is able to use both IP protocol versions:
smtp_address_preference = any

Then restart the postfix service for the change to take effect.

Otherwise, if your setup is IPv6 capable maybe yell at AWS, they really should be able to handle IPv6 in 2023...
If I recall correctly this log-message points to a general problem with DNS resolution from postfix point of view.

* does DNS resolution work reliably at 23:00?
* how does your /etc/resolv.conf look like - what are your nameservers?
I have applied the change suggested by t.lamprecht:

root@pve01:~# cat /etc/postfix/ |grep inet_protocols inet_protocols = ipv4 root@pve01:~# systemctl restart postfix

* does DNS resolution work reliably at 23:00?
DNS wwas working perfectly at 23:00
We have been receiving those mail without any problem until 21th April.
Since then, we only receive the mail when we execute backups jobs manually.

* how does your /etc/resolv.conf look like - what are your nameservers?
These nameservers work as our DNS servers

root@pve01:~# cat /etc/resolv.conf search nameserver nameserver root@pve01:~#

Scheduled job only execute on weekend, so I have created a new one that will execute tonight at 23:45

Javier López

We have managed to send emails corresponding to backup plans that include only a few VMs.

Our backup plans have always included at least 12 VMs, and nowadays, we have verified that emails continue to get queued. We think this happens because of their size.
In total, there are almost 200KB of text (each mail), and it is sent simultaneously in plain text and HTML (loglevel INFO)

Has there been any mail verbosity/format change related to a recent product update?​
Is there a possibililty to modify emails by attaching the body of the email as an attachment?​
Could we change the emial subject? Currently, all the mails of all the backup plans are the same and we cannot distinguish them. WE have to read the body of the mail in order to indentify de backup plan.​

Thanks again.


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