==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.5.2
- Deployed with iRedMail Easy or the downloadable installer? DI
- Linux/BSD distribution name and version:  Ubuntu Focal/Jammy 2 servers - same issue
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Web server (Apache or Nginx): nginx
- Manage mail accounts with iRedAdmin-Pro? no
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====
From syslog:

May 12 08:41:08 mail postfix/pipe[4268]: 4KzbQT2lyJz3xmP: to=<richard@gwadilo.com>, relay=dovecot, delay=467, delays=467/0.16/0/0.12, dsn=4.3.0, status=deferred (temporary failure)
May 12 08:41:08 mail postfix/pipe[4260]: 4KzbTW2f0Cz3xmT: to=<richard@whitneys.co>, relay=dovecot, delay=309, delays=309/0.16/0/0.14, dsn=4.3.0, status=deferred (temporary failure)
May 12 08:41:08 mail postfix/pipe[4238]: 4KzZlG2bRSz3xm7: to=<richard@whitneys.co>, relay=dovecot, delay=2298, delays=2298/0.16/0/0.16, dsn=4.3.0, status=deferred (temporary failure)

Let me explain my situation:
I tried to setup mail at AWS on an EC2 instance, but could not send mail due to a blocked port 25.  After much hair-pulling, I decided to go back to my original server by updating the MX records at the registrar.  Now, I get the mentioned error when setting up mail in Thunderbird and accessing it through roundcube.  What do you think?