Run the following command: select * from emailqueue order by eqadded desc limit 100

The EQModule column tells you which module is sending the email. If the module is machine type specific (FOCAS / Mazak / Etc), then it is an alert being being such as an excessive amount of time in a status or macro variable. If this is the case and you want to find out which machine, add {CNC} to the body of the email profile sending this email.