From Instructure regarding tigermail.auburn.edu and auburn.edu addresses:
Canvas now verifies incoming mail sender addresses against the address originally sent from a Canvas notification. This change may affect institutions that may use an additional email from their mail account, such as domain.edu and mail.domain.edu; any replies originally sent from Canvas with the simple domain would be returned to Canvas as the additional domain. If users are not able to view their email replies in Canvas, their account may have been affected by this email verification where Canvas cannot recognize both mail accounts as the same user. Users can update their email address for notifications in their Canvas user account and match the email with the incoming mail sender.
This change resolves a fixed bug in Canvas:
Explanation: When a user received a notification that can be used to reply (such as conversations and discussions), the user was able to forward the notification to a third-party user, who could reply to the email and have the reply appear in Canvas. This behavior allowed people other than the original user to reply to the notification and occurred because Canvas was not verifying the incoming mail sender. Canvas code has been updated to verify incoming mail and not allow replies from third-party senders with a different email address.
Additionally, this change also resolves extraneous email invitations that can be created through social networks such as LinkedIn. Canvas email notifications are viewed as an individual contact that can be invited to join these social networks. Canvas notifications are also picked up as a contact when a social network asks to review email addresses in a user’s address book and send invitations to non-enrolled users.
I notice that your account matches the situation described in the release notes, as you have both your …@auburn.edu and …@tigermail.auburn.edu addresses listed. My guess is that this is happening because your *sending* email address (as configured in your email client) does not match the email address to which we sent the specific notification message to which you’re replying. Your sending address seems to be the …@tigermail.auburn.edu address (based on the emails you’ve sent in connection with this case). I’m guessing that the situations in which you can’t get your emailed message-replies to go through happen when you are replying to the version of the notification message that we sent to your “…@auburn.edu” address.
You currently have your account configured so that we’re sending a copy of each notification you receive to each address. Would it cause any problems for you to disable the notifications to the @auburn.edu address so that we only sent messages to the @tigermail.auburn.edu address? That way, you could reply to any notification you received without having to worry about which address we sent that particular copy to.