The email whitelist module allows you to specify email rules for users who don't need to be approved after registration.
You can define these rules at: Administration -> Users -> Settings -> Whitelist.
The email mapping feature allows you to specify email rules for users which will be automatically assigned to a specified group after registration.
You can define these rules at: Administration
-> Users
-> Groups
-> Select a group
-> E-Mail Mapping
.
See Professional Edition licence for details.