Openproject/community:11.2.2 installed with docker plugin in Plesk Obsidian v18.0.34 on ubuntu 18.04

I'm new to openproject and docker so i don't know how to troubleshoot this. If anybody could help me it is much appreciated 

I have the following problem . If i create a user and select to send the password by email there is a notification that it is send but i don't receive the mail. There is also no activity or errors in my maillog on the server. Also if i click on invite user the email won't be send.

In the email configuration everything is set and test email and task notifications are send and received.
Right now the only way to register a user is do it manually and send them the password manually. 
Password reset also does not work, no mails received for that also. 

What can i do to troubleshoot this, any suggestions ?

Kind regards 
Gunther