Hello!
I've been using Trello for more than the year now, and suddenly the notifications stopped to arrive to my email box. In the settings "immediate notifications" are chosen, so I do not understand why that is going on. That happened to all of my collleagues who use Trello.
I think you need to contact support at https://trello.com/contact - it is likely your domain is either being blocked on our end or our emails are being blocked on your end.
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