Linuxserver/cops sendtomail.php 500 error

Hey guys,
i am running the latest build of linuxserver/cops from dockerhub, but i have since the last version troubles sending mails to devices.

the mail settings are still the same and other containers also send from this mail with this credentials.

if i inspect the sending in developing mode, i get a 500 internal server error after clicking the send button.

do you have any ideas or tipps for me?