Triangle with exclamation point inside

I didn't see a answer to this question, I wanted to let someone know what I found. I kept messing around with the different email addresses I had going into my Mac mail so I wouldn't have to go online to check Yahoo emails and a couple of others. I opened Mac mail preferences and in the accounts tab I discovered that I had 2 email accounts that I wasn't even using anymore. I think I had signed out of the accounts online. Anyway when I removed these accounts from my Mac mail accounts list, the triangle was gone.