>Is there a rule to determine if an email address is valid? I mean, just checking the characters of the address.

Brian's already mentioned the six character minimum so I won't bother with that. Try

oRE = CREATEOBJECT("VBScript.RegExp")
oRE.Pattern = "\w+\@\w+\.\w+"
? oRE.Test(tceMailAddr)

As you might guess, the Test method will return a logical value indicating whether or not the parameter matches the Pattern property.