Change e-mail address of an existent user

Hi,

I have a qmail-ldap installation + vpopmail. I need added an extension  
to some users in his e-mail address,  as I show here:

now: [email protected]

I need: [email protected]


The problem of create a new user is migrate all user info. If I create  
an alias, user could continue login with old username, and I want that  
both only work in parallel during a period of time, but then, only new  
address should work.

Have you any idea?

Regards,
Spamis