If this helps at least one person avoid our most recent headache, it's a win.
Some of our domains use GoDaddy Workspace email for a myriad of reasons. (yeah, I know, groan)
GoDaddy has been migrating customers' email over to Microsoft Outlook 365
Our accounts were recently moved to Outlook365, and all inbound email stopped.
We received NO new email from those domains after the migration.
For simplicity we were using the "catch-all" feature of the previous system.
So any email sent to firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, etc. went into one inbox, eg:firstname.lastname@example.org
We have quite a few social media accounts, all used unique email addresses when registered:
email@example.com, firstname.lastname@example.org, email@example.com all going to firstname.lastname@example.org, this worked for instagram and facebook
Same with affiliate programs.. email@example.com, firstname.lastname@example.org went to email@example.com Which is great for tracking, and easy to manage.
This functionality is not allowed in Outlook365. ALL messages not specifically sent to an existing email address will bounce with
"Your message to firstname.lastname@example.org couldn't be delivered. Returns wasn't found at domain.com. Unless specific/individual aliases for the addresses being used in the wild are assigned to existing accounts.
We found a quick and fairly painless solution by using php's IMAP functions, and parsing the 'To:' field from all the 'received messages' on the email server, and building an list of all the aliases being used to be sure we didn't miss anything.
Hope no one else experiences this.. it can ruin a perfectly good day.
If anyone has questions, just ask.