Currently we miss 2 required packages in CentOS 8.1, and i need your help to make it happen.
postfix-pcre. Used by Postfix for PCRE (Perl Compatible Regular Expressions) support, you can verify it with command "postconf -m". iRedMail uses several PCRE lookup tables. According to RedHat 8 document, postfix-pcre is available, but it doesn't. There's also a bug report in RedHat buzilla, also user report in CentOS forum.
uwsgi (and all its sub-packages like uwsgi-plugin-python2, uwsgi-logger-syslog). uwsgi is a WSGI server, used to run mlmmjadmin, iRedAdmin(-Pro). Latest Fedora release has uwsgi packages, there's bug report in Red Hat bugzilla (reported few months ago). I sent email to uwsgi (EPEL) package maintainer about 1 month ago, no reply yet. If there's other (Python) WSGI server like "gunicorn" available, we can adopt to gunicorn too, but neither exists.
I need your help to contact package maintainers to help submit the packages. They all were present in RedHat/CentOS official repo of EPEL for RedHat/CentOS 7, it should not be hard to build it on 8.
There were more missed while CentOS 8 was released, e.g. dovecot-pigeonhole (sieve server), postfix-ldap, but they are available now.