Exchange server: send mail using alias

I use different domain addresses (ie a@aa.com a@bb.com), alias of the same exchange mailbox. DNS MX records for 'aa.com' and 'bb.com' points to the same exchange server. Receiving mails works perfect, the issue is sending mails.

How can we setup outlook and/or exchange to allow us to send mails, using a different 'from' and 'reply to' than the primary address associated with the mailbox?

By default, using just the alias on the 'From' (Outlook client) the message bounce back:

#MSEXCH:MSExchangeIS:/DC=com/DC=xxx:EXCHANGE[578:0x000004DC:0x0000001D] #SMTP# 

Create another server mailbox, 'forward' incoming mail to the primary and allow 'send as...', is not the answer.

As far as Exchange is concerned, you have one email address for outbound email -the default. Any other addresses are aliases for inbound only. If you want to send using one of the other addresses, then you need to attach it to another option.

The option you have said is "Not the Answer" I am sorry to say is the only answer without third party tools. Why are you against that solution? It works very well, and doesn't involve an additional CAL. If you want to go down the third party path then Choose From is the main tool.

Simon.