If you're having trouble with the processing of incoming emails in Deskpro On-Premise, you can enable logging to see what's happening.

You can run the following command from the command line to see email processing output in real time:

php bin/cron --verbose -j process_email_gateways -f

--verbose to generate output
-j to only run the process emails job
-f to force running regardless of timers (eg to run more than once a minute)
 
You can also enable the cron log (same as --verbose but logs to a file). Add this to your config.php:

$DP_CONFIG['debug']['write_cron_logfile'] = true;

This will log everything that happens when the cron job/Scheduled Task runs, which includes email processing, to /data/logs/cron.log - disable this once you are finished troubleshooting.
 
And to log ticket filter matches and notification events, add this to config.php:

$DP_CONFIG['debug']['ticket_change_logger'] = 1;

Logs to /data/logs/ticket-change-tracker.log
 
This provides data for tickets created by email as well as changes made through the agent interface.