Why is Mattermost reaching out to remote server https://pdat.matterlytics.com

To help Mattermost improve the quality, security, and usability of our applications the suite is configured to send anonymous Usage and Diagnostic data. 

Disabling Error and Diagnostic Reporting

This server is contacted by the Mattermost Error Diagnostics and Reporting Feature. Administrators can disable it by going to System Console > Environment > Logging > Enable Diagnostics and Error Reporting

Full details on the data that is collected can be found here:

https://docs.mattermost.com/manage/telemetry.html#error-and-diagnostics-reporting-feature