Mail notification does no work with german SMTP server

I configured SMTP notification as documented on the home-assistant web page. But when I use a german SMTP, like smtp.1und1.de, I’am not able to see the notification under: Developer tools > Services.
If I change the server address to: smtp.1und1.com, then I see the notification.

Is this a known issue? Does HA only support .com mail servers?

No, your SMTP server must be dropping out rejecting the mail for any number of reasons

AFAIK the SMTP component adheres to the SMTP RFC and should work with any compliant server

sorry, found the issue, credentials.
PICNIC problem :wink: