When a mail is sent to Service Desk and is processed by maileater, what happens when the given mail does not match any of the mailbox rules established?
If the mail does not match any mailbox rules, a copy of the mail will be stored in the "$NX_ROOT/site/mail_unknown", provided the 'Save Unknown Emails' setting is activated in the Service Desk Mailbox. If this setting is NOT turned on, no storage will be provided to the mail and the mail itself will be lost.
Regardless of the mail and if it translates to a new case or update, any mails that are received by Service Desk are deleted from the given INBOX that Service Desk/Maileater is monitoring.
If a prior mail that did not pass maileater rules of of interest, the suggestion is to contact the mail administrator to see if the received messages are available in the mail server's archives.