*raises hand* So I work in IT Operations for a Large Tech Company and I used to work in the group that helped manage our email, and there is just so much of it that it's really hard. Whitelisting only works for specific IP addresses or addresses; if those keep changing, or if the protocol used for them changes, the whitelist is no longer accurate and you have to update it. This is actually an issue we've had at work a few times, where the ops guys think something is whitelisted and it actually isn't and then things break.

Most email providers on the scale of Outlook or Gmail or whoever do have a process for getting yourself unblocked, but it's generally really opaque and there's no guarantee the results will last (as DW has seen).

Like you, I forward my gmail notifications to my Outlook account, so this just adds more delay but I'm out of providers and have no wish to set up a new account...