Nothing to do with tapatalk, it's Microsoft being stupid with our registration emails. We've deployed all the correct stuff (SPF, DKIM, DMARC) to ensure that our email is not seen as spam and it is handled normally by all the other services. However for some reason MS considers it bad and messages are silently discarded on their side (we deliver it successfully to them). Sadly the MS help portals are deliberately vague to avoid assisting spammers and are thus not helpful. I have a professional background architecting huge-scale email infrastructures, and honestly, I can't fathom out why they are blocking us.
As far as I know, for ms, new domains or ip addresses start out with a poor reputation and you have to build it. With Google and yahoo, they start out with a decent one.
Therefore it's pretty common for emails from new domains or ip addresses to get marked as spam by Microsoft at first. You have to click on "not spam" in Hotmail or outlook a few times before they start going into the inbox.
I experienced that multiple times with Microsoft and it's really annoying.
Edit: I keep a few Hotmail and Outlook accounts active just for this purpose. Whenever I set up emails with a new domain or ip, I send a bunch of emails to those accounts and hit "not spam" until they start going into the inbox.