change from to email template

Hi all

I need to reconfigure mail accounts in my server.

I need to user this email address format:

Now I using:

I did all server changes for that and new account works.

My issue is with old accounts.

I’ve restored a backup with old account using the new mail template and not works, still in old format.

What’s I doing wrong ? It’s possible to change the old format to the new ?

Thanks in advance