I have a free 1 month trial of Office 365 and thought I'd see how it might handle my two gmail addresses and a third party email address. My first  gmail address worked well (once I made a few tweaks to ensure deleting emails also removed then from the gmail "All Mail" folder) so no problem there.

But my second gmail address also picks up mail sent to my third party email address. It has been configured using the "Send mail as"  and "Reply from the same address to which the message was sent" gmail settings so that when I reply to any email coming into my gmail inbox that was addresses to my third party email address if will use that address as the from address.

I have managed (after two days trying) to setup Outlook 365 to allow me to manually select the third-party address as the From address but I want Outlook to "Reply from the same address to which the message was sent" by default as per gmail. There does not seem to be a setting for this. Does anyone have any tips on maybe configuring a rule? Or maybe macro if absolutely necessary?

By the way, to allow me to send from the third party address but not have a separate set of folders I had to set up a separate pop3/smtp email profile in Outlook 365, make sure it didn't delete emails from server (so they would be picked up by gmail) and didn't save send emails. I think needed to configure a rule  to save a copy of sent email to the gmail send email folder so that I had a record along side all my other emails send from gmail itself.


In summary, my questions is: How do I make Outlook 365 "Reply from the same address to which the message was sent" by default as per gmail?