452 4.5.3 Too many recipients with Outlook 2003 and POP3 server

Mail servers sometimes limit the number of recipients in any given message.  Helps prevent spam from being sent through there servers.  Send the message twice, once each to half the list of recipients, see if that works (contact the ISP to find out what your limits are).

I asked the user to split the recipients in half and send the message again.  I will let you know what the results are later today.

I received this same error while sending to 2 recipients at the same time! I checked with the 3rd party email domain hosting service we use, and they said they do not limit the number of recipients. Therefore, this must be somewhat of a bogus error. I'm running Outlook 2003 (Office 2003 Professional). I checked, and there are no spam settings set to limit my number of recipients.

I did the only logical thing when there's an error, which was to download the latest Office 2003 updates - one of them being related to spam. This "may have" fixed the problem - which hasn't recurred since the update (it's been less than 1 day), but I'll keep my fingers crossed. I've sent several, multi-recipient emails since but I'll ask the user (I'm the sysadmin at this small non-profit co.) to try and reproduce when she works tomorrow (12/17) and I'll re-post the results after that.

While my answer was, in my opinion, a perfectly valid answer, it did not solve this question.  Given that, I would suggest mdrummond be refunded his points and the question PAQ'd - hopefully after mdrummond posts the results if he's so kind.

One of the service packs for office 2003 limits the number of outbound addresses in an email to reduce virus and spam attacks.

This is a followup from my last post to close the loop.

This (below) is the Office 2003 update I did - but again, I cannot be sure if this is THE act that stopped the "several failed messages with 452 4.5.3 Too many recipients errors". I can only say that for me it wasn't a server limitation. I also want to add that this error had happened at least a dozen times over the course of 5 days prior to my installing the listed updates:

Updates for Office 2003 products
   Update for Outlook 2003 Junk Email Filter (KB873362)
   Update for Office 2003 French Grammar Checker (KB873381)
   Update for InfoPath 2003 (KB887982) - English version

The user has happily confirmed that this error has not recurred.

A quick thought on the prior comment: "One of the service packs for office 2003 limits the number of outbound addresses in an email to reduce virus and spam attacks." I doubt that 2 recipients (or 5, as in another email for which the error appeared) would be considered outside the limit instated by the service pack; however, it wouldn't surprise me if there was a bug (which only rears its head under certain configurations) in that service pack, and so promotes a "false positive" callback from the spam-checker limit routine. One can only suppose...