A user has noticed that some emails are being discarded and not creating tickets. Upon checking the email parser logs, it displays the following failure message: "Email is being discarded since we may already have a ticket created for it, this is likely to occur when we have more than one EmailQueue address in the email recipients list".
The likely reason to get this failure message in the Email Parser Log is when an email has been sent to multiple Email Queues and the option to 'Create multiple tickets for all email queues' is disabled. This is done to avoid creating multiple tickets from the same email.
Having said that, if one encounters this problem and needs to have the same email handled in different tickets, one can enable this option from Admin CP > Settings > Email Parser > Create multiple tickets for all email queues.
If the affected email was sent to a single email queue but is still showing that failure message, it is possible there was a problem with the email processing, and it is recommended to ensure the email is valid (e.g. meets the email size constraints). One can review the email queue mailbox to look for emails that might be invalid.
If run into this problem and it doesn't seem to be related to the setting or a specific email, it is recommended to check whether any customizations have been made to your installation's PHP code.