ISA Server Alerts: SMTP

Hi! ISA e-mails me dozens of alerts every day relating to SMTP. Is that normal, 
or should I configure something different?

Alerts I get are of two types:

ISA Server alert: The SMTP command exceeded its allowed length
   ISA Server name: ISA-SVR-1
   NOOP

or      

ISA Server alert: An unknown SMTP command
   ISA Server name: ISA-SVR-1
   XEXCH50 1840

Thanks so much in advance for any insight into this!

Alfonso

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