Problem:
SQL mail stops at any time during the day on Standard Edition servers

Scenario:
5 SQL SERVERS (2 Enterprise and 3 Standard Edition)
All servers use lastest service packs for SQL and and Windows

ALL servers use same mail server , same domain account to run SQL service

My "solution" when Mail stop working

I retype password for SQL service accountin EM, it force SQL service and agent to restart and mail start working again till ....it stops again 10-15 hrs after.

Where to look for problem ?

thank you.