I guess plesk, or the provider of the Smartermail module for plesk, needs to update their plugin so it works with latest builds.
You should contact plesk about this.
According to the error it seems that the module tries to determine the SmarterMail version automatically, using some API endpoint on the SmarterMail server that is now probably not accessible anymore.
Sébastien Riccio
System & Network Admin
https://swisscenter.com