==== Required information ====
- iRedMail version (check /etc/iredmail-release): 2.4.1
- Linux/BSD distribution name and version: Centos 7
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Web server (Apache or Nginx): nginx
- Manage mail accounts with iRedAdmin-Pro? : Yes
- Related log if you're reporting an issue:
====

Hi first off great product. Having said that I have a bit of a weird request.

Some background info on my situation.

I have one old email server which is going to be replaced by iredmail. There are over 700 users and multiple domains on the old server that is to be moved over to the iredmail server.

We are planning on migrating it in stages as all users are scattered all over and comes in back to HQ periodically.

I was wondering if i can have the iredmail relay the emails to the old server while retaining a copy of the email itself so users can actually use either servers. Once we have every user using the new server we will decommission the old one then.