Convert to CT

Yes,of course,create a CT,and then copy everything similar to this:
rsync -aAXv --exclude={"/dev/*","/proc/*","/sys/*","/tmp/*","/usr/tmp/*","/run/*","/mnt/*","/media/*","/var/cache/*","/","/lost+found","/boot/"} /* root@172.16.0.249:/
Just test of course.
 
Then just copy everything and see that postfix is working with new ip address. Then stop postfix,sync everything and this is it.