e-mail notifications will not be sent

[cerebellum98]

I use an outlook e-mail address to send notifications via formR. I repeatedly receive feedback that the subjects have not received an e-mail. No error is displayed in the overview on the formR website and the item is shown as “completed”. However, no emails are sent.
The same applies when I test the notifications in the run settings. No mail is sent here either.

Does anyone have any experience with this?