Maximum Length of a URL

Working on some ASP.NET, and making an email list that prints to the screen. Easy enough. But they want to click on a URL and have it auto email (BCC specifically). so..

<a href="mailto:?bcc=list of emails">Click here to Email</a>

but some email lists were huge, some small. By trial and error and searching around Google, I figure around 2000 characters is the optimal length for the “list of emails” I tested in IE6 and Firefox 3.01 and the same result for both. If it is longer, the link just doesn’t work at all. If you are close the boundry in IE 6 you sometimes will get a “Mail client” error, but I am guessing that is because of the mailto: in the link.