I am using Exchange 365 as my mail server - I have my mailbox set up to retrieve primary email from my domain address and also I have two receive connectors set up to receive email from Hotmail and GMail respectively.
The issue is that while exchange 365 can receive email from multiple accounts into one mailbox, it can only send via the primary address. Outlook 2013 reports that it is sending using the 'correct' from address, but the recipient gets an email with a different 'from' address and a message 'sent on behalf of abc'. For example, if my primary email is email@example.com and my GMail account is firstname.lastname@example.org outlook will say sending from 'email@example.com' but the user will receive an email from firstname.lastname@example.org sent on behalf of email@example.com'
This creates two problems - first of all it breaks any application that is tracking email conversations and rely on the correct from address - for example I have found that I cannot respond to message sent via eBay.com as it requires the email to be sent from the registered account (in my case GMail) - I have to log into gmail, cut and paste the old message from outlook resulting in losing the message history. Secondly, often the purpose of additional accounts is to segregate messaging - for example using one account for business and the other for private. Because the recipient receives both email address one can find one getting spam to ones private address or business communications turning up in the wrong place.
I think this issue has been raised by others in this forum and my feeling is that it is rather a glaring issue. I am wondering if there is a way of reporting it as a defect to Microsoft that does not involve long discussions with non-technical people in public forums. Perhaps it might benefit from being fast tracked through tech-support.