==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release):

root@parakeet:~# cat /etc/iredmail-release
1.3.2 PGSQL edition.
# Get professional support from iRedMail Team: http://www.iredmail.org/support.html

- Deployed with iRedMail Easy or the downloadable installer?

yes

- Linux/BSD distribution name and version:

root@parakeet:~# uname -a
Linux parakeet 5.4.0-88-generic #99-Ubuntu SMP Thu Sep 23 17:29:00 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

- Store mail accounts in which backend (LDAP/MySQL/PGSQL):

PGSQL

- Web server (Apache or Nginx):

nginx + apache2

- Manage mail accounts with iRedAdmin-Pro?

no

- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.

root@parakeet:~# mail -s "test subject" rene.veerman.netherlands@gmail.com < /dev/null
mail: Null message body; hope that's ok
root@parakeet:~# tail /var/log/mail.log
Oct 11 13:42:14 smtp amavis[1330]: starting. /usr/sbin/amavisd-new at smtp.nicer.app amavisd-new-2.11.0 (20160426), Unicode aware, LC_ALL="C", LANG="en_US.UTF-8"
Oct 11 13:42:14 smtp amavis[2543]: Net::Server: Group Not Defined.  Defaulting to EGID '144 144'
Oct 11 13:42:14 smtp amavis[2543]: Net::Server: User Not Defined.  Defaulting to EUID '136'
Oct 11 13:42:14 smtp amavis[2543]: No ext program for   .F, tried: unfreeze, freeze -d, melt, fcat
Oct 11 13:42:14 smtp amavis[2543]: No ext program for   .zoo, tried: zoo, unzoo
Oct 11 13:42:14 smtp amavis[2543]: No decoder for       .F   
Oct 11 13:42:14 smtp amavis[2543]: No decoder for       .zoo
Oct 11 13:42:14 smtp amavis[2543]: Using primary internal av scanner code for clamav-socket
Oct 11 13:42:14 smtp amavis[2543]: Found secondary av scanner clamav-clamscan at /usr/bin/clamscan
Oct 11 13:49:09 smtp amavis[3193]: (03193-01) Passed CLEAN {RelayedInternal}, ORIGINATING LOCAL [127.0.0.1] /ESMTP <root@smtp.nicer.app> -> <rene.veerman.netherlands@gmail.com>, (), Message-ID: <4HScX4546BzbbgB@smtp.nicer.app>, mail_id: LQg_C_umuBOq, b: 1B2M2Y8As, Hits: 0.379, size: 344, queued_as: 4HScX54NThzbbcm, Subject: "test subject", From: <root@smtp.nicer.app>, X-Mailer: mail_(GNU_Mailutils_3.7), helo=, Tests: [NO_DNS_FOR_FROM=0.379,NO_RELAYS=-0.001,TVD_SPACE_RATIO=0.001], autolearn=no autolearn_force=no, autolearnscore=0.38, dkim_new=dkim:nicer.app, 746 ms
root@parakeet:~# tail /var/log/mail.err
root@parakeet:~#
root@parakeet:/var/mail# ls
root@parakeet:/var/mail#
root@parakeet:/var# nslookup smtp.nicer.app
Server:         127.0.0.53
Address:        127.0.0.53#53

Non-authoritative answer:
Name:   smtp.nicer.app
Address: 80.101.238.137
Name:   smtp.nicer.app
Address: 127.0.0.1

====

i have no idea why mail isn't being delivered. please let me know if you need more info from my system.