When using maileater to check a mailbox and generate tickets, it will fail to generate a ticket if the "from" email address is not tied to a valid contact record in Service Desk. A condition may occur when it appears that maileater is not generating a ticket even though the "from" email address appears to be tied to a a valid and active contact record in Service Desk. This can be caused by mutliple contact records and/or groups having the same email address attached to them.
Do a search on the ca_contact table, using SQL or Oracle tools, for the "from" email address and ensure that it does not appear in more than one row. If it does, then edit those contacts and/or groups so that only one record has that email address attached to it.