Dav just pointed out to me that there is a public Adobe HotFix for the ColdFusion 8.0.1 CFMail problem that was causing this error in my mail log file:
The ColdFusion Mail Spool Encountered An Invalid Spool File In The Spool Directory. The invalid file MailXXXXXX.cfmail was moved to the undeliverable directory.
I just downloaded the HotFix, installed it, and moved the undeliverable emails to the Spool folder. They were all sent out, no problem. There were about 40 or 50 emails in there, so sorry if you are now getting emails from a week or two ago.
Thanks to Dav for bringing this to my attention!