Not receiving Registration confirmation email

[JHA]

Hello,
after successfull registration of several devices with my T-Online.de email I am now not receiving a otp email for new registration of an android device. Because my Gmail Email ist different from my T-Online Email I can not sign in with Google Account. I checked all SPAM folders and disabled SPAM detection in email settings. I think there is a general issue with T-Online.de emails because if i use a different domain I receive the email but can not register because my Google account is already linked to my T-Online Email.

What should I do?

This is really disappointing because I paid for enpass on Android, iOS and Windows in the past year.