==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release):  1.4.0 MARIADB edition
- Deployed with iRedMail Easy or the downloadable installer? installer
- Linux/BSD distribution name and version: Ubuntu server 20.4
- 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.
====

Hi All

Firstly thank you to the developers and supporters of this product.

I am completly new to iRedMail and linux and I have been banging away at this problem for 12 hours and admit defeat.

I have iredmail installed and everything seems to work. 
Web mail works for inbound and outbound. 
port 25 143 443 and 587 are forwarded through my firewall to the mail server
The server host name is mail.mydomain.com
I have a LE cert installed and it works in Nginx (no errors on webmail page) and correct cert visible
I have added the cert to Postfix and Dovecot by using the symlink method described here: https://docs.iredmail.org/letsencrypt.html
The cert is issued to mail.mydomain.com

However when I try to set up a Thunderbird email client (user=myname@mydomain.com) I get an error (see attached) about adding a security exception for location "domain.com" Even though the cert is correctly issued to MAIL.domain.com.  The attached shows a screen shot of the error with the certificate in question in the background.

The second attachment shows the setting I am using on the client.

Any suggestions as to how to resolve this would be appreciated as I am stumped.