function to inhibit sending email using the wrong user-mail-address?

[Frank Fredstone]

On a couple of occasions I have sent email to my work using my home
email address and sent email to non-work related people using my work
email address, and I don't want to do that again.

I'd like to write a function to prompt me if I have a
user-mail-address set the wrong way when sending to someone who's
address matches some pattern or goes through some filter like the
splitting mechanism.

What is the best way to write such a function?  Should I bind the key
sequence I use to send email to my function, or does a callback exist
already? Do I get access to the headers of the mail I'm sending by
searching the current buffer, or is there another way?