Question : large list best practices

I have a large list of about 200 people that are affiliated with my organization.  I currently have a 50 recipient per message limit, which I am told is part of best practices for the sending of e-mail, and it really ticks users off.

I am looking for reliable references that back up the 50 recipient limit, to sort of convince users that the limit isn't in place because "the admin said so".  Please link to any reliable best practices lists and pages that you know of.  Thanks!

Answer : large list best practices

Here's more general info: http://support.e-zekiel.com/templates/Manual/details.asp?id=31606&fetch=26546

Check Google for "email sending limits" http://www.google.com/search?q=email+sending+limits and you'll see that most web hosts and ISPs have limits.