Can't transfer because of incoming mail?

Hi Blizzard and fellas

I'm having a problem, I'd like to transfer my toon to this new server because I was invited to raid with one of the top guilds. However it says I can't because of mail I haven't received, first I checked my mailbox and I had some mail, I deleted it. Now I try again, and it says the same. Does this have like a time to update my character's mailbox? How do I know if I have incoming mail?

I'd like a blue post on this.

The character I want to transfer is Konstantine in the server Quel'Thalas (Latin America)