Have you ever wondered why emails are not being delivered but keep building up in your ColdFusion spool folder? If so you have then probably seen an error message to this effect:
cfmail spool folder not processing MailXXXXXX.cfmail files.
This really got me going, one minute the emails was working and next minute it all stopped and nothing had changed. Being a live server the emails kept building up in the spool folder. Evenutally I figured out a solution or two.
A lock in the system can sometimes cause this kind of a behaviour. The first point of call would be to restart your ColdFusion Server. If this does not work then you need to look for the 0byte folder in your spool folder, this will be a corrupt file, remover this and you will see all your emails being sent out.