Gmailevolent

I recently ditched Apple's Mail program for Gmail once I found out that I could forward all of my email to that address and it would automatically set me to that address on replies. This works rather well for most things, except when I want to send a second reply. Whatever figures out which email to use only looks at the "To:" area from the previous email, even if I sent it. This led me to email someone an addendum from a different address. I'm sure that was confusing.