Q: For some reason MAIL is not sending to addresses I put in the BCC block.  Any idea why?

Hello Cherylolson1524,

This definitely sounds like a strange issue with your emails not being sent to recipients you put into the BCC section. I would first force quit the Mail app completely, relaunch, then check to see if this occurs with a different Mail account if you have multiple accounts setup. If you do not, try to Start up in safe mode. Safe mode (sometimes called safe boot) is a way to start up your Mac so that it performs certain checks, and prevents some software from automatically loading or opening. If the issue is not present in safe mode, this may mean that an application running in the background is causing the issue. You can remove login or start up items by following the steps in this link. OS X Yosemite: If you think you have incompatible login items 

Once all the login items are removed, please restart your Mac normally then test the Mail apps BCC sending capabilities. Thanks for using Apple Support Communities to post your question. 

Have a good one!