[Dovecot] Special user

[Daniel L. Miller]

Not sure what to call this - I'm actually working out the details as I 
type this.

I want to have a valid username/password for an account for sending 
purposes - but when receiving this is an alias that broadcasts to 
several users.

Example:  accountspayable at mydomain.com - is an alias for 
jane at mydomain.com, june at mydomain.com, and john at mydomain.com.  However - 
any mails sent (from a particular client software) should all only show 
"accountspayable" as the sender.

How would I implement this?  I'm asking here because Dovecot serves as 
the authentication mechanism for my SMTP server (Postfix) via LDAP lookups.

-- 
Daniel