timezone in rexx

Hi,

I ran a special CLIST in mainframe where i had TIMEZONE = EST in SMTPNOTE. While receiving the mail, the timestamp in the mail has one hour delayed time, whereas when i changed it from EST to EDT it worked fine.

Can anyone help me out to find difference between EDT and EST in this case?
Also let me know what time will mainframe take if we set the TIMEZONE as EST.

Thanks,
Kumar