The other day my mom received an e-mail sent by a friend. Outlook told her:
“From: firstname.lastname@example.org on behalf of email@example.com.”
She was like, “Was this e-mail really sent by my friend? It is a different sender address *wondering*?”
I explained her that the person used Hotmail to send the e-mail. Hotmail uses its own servers to send messages. Since you can use your own e-mail address with Hotmail, problems might arise if a message appears to be sent from your e-mail address, but not from your server (from Hotmail’s server instead).
This is why Hotmail is respecting the sender authentication and is using both the From and Sender headers to indicate that the mail was sent correctly. Yet, using these headers results in the On behalf of view in some e-mail programs, including Microsoft Outlook. The On behalf of line, however, is what makes people like my mom wonder what this is all about.
Yet, there is an easy solution to fix this. How? To get an idea, let’s take a look at how Google has solved it with Gmail. Look at this photo:
Instead of sending messages through Gmail’s servers, you may choose to send e-mails via your own SMTP (outgoing mail) server. This way, there is no authentication problem, as messages are only sent from the “correct” server.
Question being—why doesn’t Hotmail offer the custom SMTP feature? You may well receive messages from other accounts using POP, so why not send them via other accounts using SMTP? That’s one of the unanswered questions I have in mind.