Your message was not sentOf course I've contacted "The Yahoo! Mail Team" multiple times and I've changed my password. So far nada and now the problem is starting up on another Yahoo mail account that I forward spam messages from.
Your account has been temporarily blocked from sending messages. This block can be caused by sending messages that trigger our spam filters, or by having too many recipients in one email. We encourage you to review the contents and recipient list of your message, and try sending it at after an hour or two. Doing so will usually resolve the matter.
If you are still unable to send messages after a 24-hour period, please read our FAQ for more information and to request Customer Care assistance.
We apologize for the inconvenience.
The Yahoo! Mail Team
This issue is especially problematic with SpamCop because after 24 hours the timestamps in the headers of the spam messages become stale and SpamCop won't process them, so I end up deleting most of them. It's a sad irony that my endeavors to help in this fight against spam are being thwarted by the very Yahoo feature that is itself trying to protect email users by identifying spam sources within Yahoo mail. While I totally understand the purpose of this effort and applaud the work being done; In my case it's overreaching and needs to be tweaked in some way. Possibly if the the application could look at the recipient email list to see if they're being sent to spam fighting organizations first before deciding whether or not to block the account.
Update (10/25/2010): After resolving the issue way-back-when the problem has re-appeared.
Update (4/4/2011): After throwing up my hands and giving up I tried again a month later and the problem went away completely. Now I have a new problem with Yahoo Classic. It keeps fouling up the send saying "There was a problem! Not sure why, but our usually-reliable server goofed-up while sending this message. Please try again." and I try again and it doesn't work. Or if it does get sent it will fail to allow me to delete the email saying "There's a problem viewing this message. Are you trying to access a message that's been moved or deleted? Try going to the folder it's in (e.g., Inbox, Trash) and selecting the message from there. If you've tried this, and relaunching Yahoo! Mail doesn't work either, feel free to contact Customer Care about Error Code 4."