What do we do, when an email does not arrive

[antonykamp]

Is your feature request related to a problem? Please describe.
Somebody could signup multiple times with a non-existing email. The senders' mailbox will overflow because we don't handle non-existing email at the moment.

Describe the solution you'd like
Maybe it's possible to verify an email and send it afterward.

Describe alternatives you've considered
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Additional context
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