So I joined in a mailing action, mailing members of the EU parliament in order to get them to vote against encryption backdoors.
Now it seems that @Tutanota blocked my account, probably because it sees me as a spammer now.
Maybe it's not the right email provider for me after all, when they're so trigger happy with the ban-button, which is rather disappointing as it's one of the few that promises real privacy.
If you're on Tuta and you want to invite lots of people to your party, you'll have to send every guest a separate email, or else risk a lock out.