==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.6.4
- Deployed with iRedMail Easy or the downloadable installer? no
- Linux/BSD distribution name and version: CentOS Linux release 7.8.2003
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):  MySql
- 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 did upgrade iredmail from 1.5.0 to 1.6.4 step by steps. Also upgraded iredadmin-pro step by steps.
All upgraded are successfully completed. But, when i'm using iredmail from web , there is internal server error appear.

it's resolved. It's glusterfs issue.
Note - i have installed one domain in two mail servers (2vms) and they are replicated(/var/vmail/vmail1) with glusterfs.

I did upgrade iredmail from 1.5.0 to 1.6.4 step by steps. Also upgraded iredadmin-pro step by steps.
All upgraded are successfully completed. But, when i'm using iredmail from web , there is internal server error appear.

Note - i have installed one domain in two mail servers (2vms) and they are replicated(/var/vmail/vmail1) with glusterfs.