The cron.php script will send out any emails that are marked as "pending" or "error" which were scheduled to be sent in the last 7 days. After 7 days, cron.php will stop trying to send out those emails.
You can stop the cron.php script from sending out those emails by changing APP_MESSAGE.APP_MSG_STATUS from 'pending' or 'error' to 'sent' in the database.
The other way to not send out the emails is to execute your cron.php
script like this without the "email" option:
php cron.php scheduler unpause plugins calculate unassigned-case
see: https://wiki.processmaker.com/3.2/Execu ... hp_Options