OK, off the top of my head - what is the normal content of the mail you send? Printed reports? If so, you might be using dtaqs to send it to mmail (via the configuration of the outq). If the dtaq is screwy, that might be causing your problem. Look for a job under subsystem qsyswrk - use WRKACTJOB SBS(QSYSWRK) - running function EMLSPLF, or some such. Work with that job - option 5 - then display the job log - option 10. Maybe that can tell you what's going on.
If not, the mailing job will prolly be running explicitly, and you might be able to find out more via dsplog.
Let me know if you find anything...