What actually happens is that Blogger only allows you post a certain number of posts by email within a 24-hour period. I am not sure what that number is, but based on trial and error, and Googling other people's descriptions of the problem, it is something like 30 or 40 posts.
Even if you have your settings so that your post-by-email posts are saved as drafts, and not immediately published, Blogger will still cut you off from posting-by-email, and bounce emailed posts back to the sender.
After you are cut off for that 24-hour period, you have to go into your blog and manually add each post, solving a captcha for each post. In the next 24-hour period, the block will be lifted and you'll be able to post-by-email again. Also, the 24-hour period is not based on the calendar day, and doesn't necessarily take 24-hours from the time you got cut off. It could be sooner than that if you emailed a bunch of posts much earlier in the day, and only "tripped" the cutoff limit later on.
What Blogger's auto-message should say is more like, "You have exceeded a limit for captcha-free, post-by-email posts within a 24-hour period. You may resume posting-by-email in about a day. To post more entries immediately, you may always login to your Blogger account and post manually."
via
http://www.google.com/support/forum/p/blogger/thread?tid=4ba296da27d64977&hl=en