Question : Sending out mass mailers to user subscribed mailing list. Getting SMTP 221 return code

Hello

we just sent out a mass mailer to people who subscribed to our (local) marketing list. I have tested the outgoing mail client which relays internally off my Exchange 2003 server. I successfully sent to all kinds of different domains. When the mass mailer was sent out, we got a lot of bounce messages with the following error:

[email protected] on 11/7/2007 2:27 PM
  The e-mail system was unable to deliver the message, but did not report a specific reason. Check the address and try again. If it still fails, contact your system administrator.
 

Most of the email domains are yahoo.com, adelphia, and sbcglobal.net, some gmails in there as well. Also some smaller domain names. I did get some 550 errors, but only 5 or 6. It appears the prodigy.net server is blocking/closing the connection. Is that true? I use Postini as a smarthost, and am configured to only send mail through (and receive from) Postini IP range. Is this prodigy/AT&T telling me they think I'm spamming?

thanks for any tips!

Answer : Sending out mass mailers to user subscribed mailing list. Getting SMTP 221 return code

I believe Prodigy is rejecting your message because there are too many recipients in your To field.
This makes you email look like spam. Try sending in smaller batches if you application allows (or sent a few manually and see if you get the same error).