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Office 365 - Problems Forwarding E-mail

Users who have opted to set up email forwarding in Office 365 have reported that some messages aren't forwarded as expected (the sender may receive a non-delivery report). The delivery failure is often the result of policies enforced by 3rd party email providers as part of the e-mail provider's measures taken to combat spam. Because the policies affecting forwarded email are enforced external to CSU or Office 365, ACNS has limited or no means to address the problem in most cases. Because of this, ACNS's recommendation is that users do not forward e-mail away from Office 365. If users do choose to configure forwarding in Office 365, it is recommended to configure forwarding options so that a copy of forwarded e-mail remains in the Office 365 mailbox.

Note that if a user has forwarding settings configured in Office 365, most e-mail will likely be delivered without issue to the "target" address the user specified - i.e. there's usually a specific set of conditions that is met, which causes a 3rd party email provider to reject a particular message. A typical example is described below where a Yahoo sender sends an email to an @colostate.edu address, which in turn forwards it to a different Yahoo address. In this case, Yahoo rejects the message because Office 365 acts a "middle man" (or "relay" in email terms) for the email, which is not allowed by policies enforced by Yahoo.

  1. An email message is sent from userA@yahoo.com to CSUUser.smith@colostate.edu, whose mailbox is hosted in Office 365.
  2. CSUUser.Smith@colostate.edu has forwarding configured in Office 365 to forward e-mail to csuuser@yahoo.com - note that the destination e-mail address is also a @yahoo address, albeit a different user on Yahoo's system.
  3. Office 365 attempts to deliver the e-mail message sent by userA@yahoo.com to csuuser@yahoo.com based on forwarding settings configured for CSUUser.Smith@colostate.edu but the message is rejected due to policy settings enforced by the receiving Yahoo server because Yahoo is ultimately detecting an Office 365 server attempting to send an email from a @Yahoo address.

While any given sender's messages may be subect to this issue, messages received from AOL and Yahoo senders (those with username@aol.com and username@yahoo.com style addresses) are particularly subject to non-delivery due to AOL and Yahoo DMARC policies.