There is a maximum length for the text in the &body section of a mailto: link. According to one of my co-workers, the W3C publish the limit as 256 (I don't have a link to back this up, though).
We're embedding mailto: links in both an e-mail and a webpage and have successfully used more than 256 characters. After a certain point, though, e-mail clients and browsers start flaking out and refusing to open the link.
I would like to know the actual maximum lengths allowed for the following:
Mail clients:
Browsers:
Any and all numbers you can provide will be gratefully received.
The standard doesn't define a maximum length, leaving implementation up to browsers and mail clients (See IETF RFC 2368).
Microsoft products do have set limits:
Other browsers are likely to work up to lengths beyond that of a reasonable email body. The iPhone doesn't have a documented limit, but works with up to 1MB of text.
Modern browsers that support data urls (everything except IE<9) should be fine.