I have configure my sendmail for multiple domains by creating username like
email@example.com firstname.lastname@example.org email@example.com
in passwd file
Now I added entry in file /etc/mail/virtusetable like
firstname.lastname@example.org sales\@domain1.com #escape to count as user not email email@example.com sales\@domain2.com firstname.lastname@example.org sales\@domain3.com
So when configuring the email client you provide your username as email@example.com,firstname.lastname@example.org etc. I tested with webmail and outlook it works.
Is this the best way to do it ?.Do i need to put the entry in any other file like genericstable.