Local Email Aliases


I have a local domain mydomain.lan, where we have a zentyal DC and NS connects AD to Zentyal to get the users from the DC. I have our external website and email, hosted with our provider at mydomain.com, and I use the pop connector to pull the emails to the local user@mydomain.lan accounts.
Internally, I do not want the users to see their user@mydomain.lan account (it will confuse them), I want them to login, send/receive with their user@mydomain.com account.
I have accomplished the sending/receiving by adding mydomain.com to the email/domain section, and then setting up an email alias for the user.
My question, is 2 part, first, is there another way to accomplish this, so I do not have to setup an email alias for every single user, and remember to add to any new user?
2nd, is there a way to have user@mydomain.com be used to login to webtop, I know I can just login with ‘user’, and I can login with user@mydomain.lan, but not .com.