Problems with Newsletter
 

Hey guys!
I use ASP to contact the clients of my website via a Newsletter. Problem is, many of those e-mails keep on coming back to me, wich is really annoying. I thought it could possibly be because of 2 reasons:
1-(less likely) Clients have been giving me wrong e-mail adresses. The solution would be cursing all of them and deleting their e-mails from the database.
2- Since the database has more than 600 e-mail adresses, the mailing server could be rejecting the huge amount of e-mails sent all at the same time. The solution could be sending, like, a group of 10 e-mails at a time.

Below it follows an example of the 1537 e-mails I received last time I sent the Newsletter:

"Subject: ENC: Delivery Status Notification (Delay)
This is an automatically generated Delivery Status Notification.

THIS IS A WARNING MESSAGE ONLY.

YOU DO NOT NEED TO RESEND YOUR MESSAGE.

Delivery to the following recipients has been delayed.

NONONONO@BLAH.COM"

What could the problem be?
Thanks!
TaviO!

It could be a network congestion, or the receiving server is overwhelmed with emails...

Then sending a specified amounts of e-mails in separated times would do the trick?
Problem is, I can't run tests on it... or else the clients would receive test e-mails and that would suck =(