No, "too many recipients" is a specific error message which will have a
specific cause. "I can't send email" is vague but "too many recipients" will
match an entry in the MS list of error messages.
It would still be useful to find out how many recipients he was trying to
send to. However I wonder whether it does the same to different ISPs - could
it be an ISP restriction rather than a WIndows Mail one.