email rejected due to domain not found

Jacky Li

Jan 15, 2019
Nov 24 06:59:59 pmxmail postfix/smtpd[450]: connect from[]
Nov 24 07:00:00 pmxmail postfix/smtpd[450]: Anonymous TLS connection established from[]: TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)
Nov 24 07:00:02 pmxmail postfix/smtpd[450]: NOQUEUE: reject: RCPT from[]: 550 5.1.2 <>: Recipient address rejected: Domain not found; from=<> to=<> proto=ESMTP helo=<>
Nov 24 07:00:02 pmxmail postfix/smtpd[450]: disconnect from[] ehlo=2 starttls=1 mail=1 rcpt=0/1 quit=1 commands=5/6

Once a while, it seems the cache dns server can't resolve the and rejected the email. I modified the unkown_client_reject_code from 550 to 450 so the other side can retry later. It happend couple of times now and usually lasted few hours each time. Somehow it resolved itself later. Any ideas? Thank you.

root@uhhepgw:/boot# uname -a
Linux uhhepgw 4.15.18-21-pve #1 SMP PVE 4.15.18-48 (Fri, 20 Sep 2019 11:28:30 +0200) x86_64 GNU/Linux
root@uhhepgw:/boot# pmgversion -v
proxmox-mailgateway: 5.2-1 (API: 5.2-7/9943bd5d, running kernel: 4.15.18-21-pve)
pmg-api: 5.2-7
pmg-gui: 1.0-45
pve-kernel-4.15: 5.4-9
pve-kernel-4.13: 5.1-45
pve-kernel-4.15.18-21-pve: 4.15.18-48
pve-kernel-4.15.18-20-pve: 4.15.18-46
pve-kernel-4.15.18-18-pve: 4.15.18-44
pve-kernel-4.15.18-15-pve: 4.15.18-40
pve-kernel-4.15.18-12-pve: 4.15.18-36
pve-kernel-4.15.18-11-pve: 4.15.18-33
pve-kernel-4.15.18-7-pve: 4.15.18-27
pve-kernel-4.13.16-3-pve: 4.13.16-49
pve-kernel-4.13.16-1-pve: 4.13.16-46
pve-kernel-4.13.13-5-pve: 4.13.13-38
libarchive-perl: 3.2.1-1
libjs-extjs: 6.0.1-2
libjs-framework7: 4.0.5-1
libpve-apiclient-perl: 2.0-5
libpve-common-perl: 5.0-54
libpve-http-server-perl: 2.0-14
libxdgmime-perl: 0.01-3
lvm2: 2.02.168-2
pmg-docs: 5.2-3
proxmox-mini-journalreader: 1.0-1
proxmox-spamassassin: 3.4.2-3
proxmox-widget-toolkit: 1.0-28
pve-firmware: 2.0-5
pve-xtermjs: 3.10.1-2
zfsutils-linux: 0.7.13-pve1~bpo1

One more thing, how do I delete those old kernels? apt-get purge <kernel package> ? Thank you.

Check the DNS-settings of - also ask every single authoritative server for, whether they have the same records for it.
On a hunch - one of the authoritative servers does not have the same data (probably outdated) and your caching server gets the wrong answers when asking it

One more thing, how do I delete those old kernels? apt-get purge <kernel package> ?
That should work - also consider upgrading to PMG6 where the old kernel versions should get removed automatically

I hope this helps!


The Proxmox community has been around for many years and offers help and support for Proxmox VE, Proxmox Backup Server, and Proxmox Mail Gateway.
We think our community is one of the best thanks to people like you!

Get your subscription!

The Proxmox team works very hard to make sure you are running the best software and getting stable updates and security enhancements, as well as quick enterprise support. Tens of thousands of happy customers have a Proxmox subscription. Get yours easily in our online shop.

Buy now!