I have had trouble sending emails when the character count for the "To" field is greater than 256 characters, so you might find that you have the same problem. You might consider making an email alias that contains all of the 350 people. That way you can use a single email address that maps to all the users.
one more thing, does teamsite allows emailing to external address such as yahoo, gmail?
ghoti, I am using iwsend_mail.ipl for emailing.
iwsend_mail.ipl uses Mail::Mailer to send the email, and Mail::Mailer accepts a reference to an array of scalars (email addresses) to be provided for the header elements (e.g.: to field) and should do the right thing - however, I'm not entirely sure how you would get iwsend_mail.ipl to know about hundreds of addresses to use ... would you enter them all in as task-level variables or command-line arguments?If you do go this route (you already said you'd probably go the dist-list route, which is probably cleaner) - then I think you'd have to create a copy of iwsend_mail.ipl and modify it to take a parameter for a file list of recipient addresses so that you could handle the processing of all those email addresses internally rather than trying to pass them from the WF to the script as individual parameters.