email rejected due to domain not found

[Jacky Li]

Nov 24 06:59:59 pmxmail postfix/smtpd[450]: connect from mail-eopbgr10080.outbound.protection.outlook.com[40.107.1.80]
Nov 24 07:00:00 pmxmail postfix/smtpd[450]: Anonymous TLS connection established from mail-eopbgr10080.outbound.protection.outlook.com[40.107.1.80]: 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 mail-eopbgr10080.outbound.protection.outlook.com[40.107.1.80]: 550 5.1.2 <receiver@domain1.com>: Recipient address rejected: Domain not found; from=<sender@cern.ch> to=<receiver@domain1.com> proto=ESMTP helo=<EUR02-HE1-obe.outbound.protection.outlook.com>
Nov 24 07:00:02 pmxmail postfix/smtpd[450]: disconnect from mail-eopbgr10080.outbound.protection.outlook.com[40.107.1.80] 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 domain1.com 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.

Jacky

 

[Stoiko Ivanov]

Check the DNS-settings of domain1.com - also ask every single authoritative server for domain1.com, 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!