No confirmation mail to Outlook.com from fediverse.

Hi, I just realized that my previous attempts to join the fediverse via Mastodon or Lemmy where just blocked by my choice on the mail provider. I never got any confirmation mail neither in the inbox nor in spam, tested with multiple servers, mask addresses. Just right now tried it with my Gmail account and got the mail instantly.
Guess this could be a problem for many new users trying to join us.
I guess the confirmation mails are send directly from the different server instances? Maybe they don't have enough reputation yet to come through outlook filter?