For compatibility issues, when migrating a domain from another different hosting, I would need to separate the suffix from the username with dashes instead of dots, that is:
Yeah you can do that… First you need to go to System Settings -> Server Templates -> Mail for Domain and set “Format for usernames that include domain” to “username-domain”.
Then you go to Server Configuration -> Change Domain Name and use “Change mailbox name suffix?” to set it to the domain name scheme you desire.