How does qmail handle multiple branch offices?

If you have multiple offices you may choose to have more than two qmail servers.

If you have two servers, one called office1.company.com, and another called office2.company.com. Setup the accounts on the servers for the local users and then create a .qmail-default file which checks to see if the user is local. If the user is local then deliver it, if not then forward it to the other server. Remember to get the .qmail-default file to check if the email has already been forwarded to the other machine. If it has, then bounce the email.

You can then set two MX records records, one pointing to each server.