[imp] (Send)mail aliases

[Lars Hecking]

> I have to manage the accounts of a hihg-school students.
> They all have mail aliases firstname.lastname@domain.com, which gets mapped
> (according to the alias file in sendmail) to username@domain.com.
[...] 
> When they use some kind of a POP3-based mailer, it works well,
> even server's mailx does the job, but when it comes to imp, it still sends
> out mail with the source address username@domain.com.

 aliases are only relevant for local *delivery*. To rewrite outgoing
 sender addresses username@domain.com -> firstname.lastname@domain.com
 you'll have to do some sort of canonical address rewriting. I believe
 this feature is called genericstable in sendmail.