==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.6.2 MariaDB
- Deployed with iRedMail Easy or the downloadable installer? Downloadable installer
- Linux/BSD distribution name and version: CentOS 7
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MariaDB
- Web server (Apache or Nginx): Nginx
- Manage mail accounts with iRedAdmin-Pro? Yes
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

I followed these instructions to disable amavisd spam filtering, virus scanning, but intentionally left DKIM signing.

1. This doesn't prevent amavisd from making database entries about emails that amavisd processes.
2. The script iredadmin/tools/cleanup_amavisd_db.py will not run if spam filtering is disabled.

Because of this the amavisd database grows over time. We had over 16M records in the msgs table which was impacting performance enough to cause queue backups and delays.