Guild Wars 2

Hi all,
i need to know if there is a method to know if your in game mail as arrived to the receiver.
I ask this because today i dropped a rare item from a mob and I wanted to sell it at trade lion company.
The fee cost was 3,75 gold but i had only 37 silver, so i asked to my guild mate if he could give me that money for the transaction and i would give him back 4 gold after the sale.
Then i wrote a new mail with 4 golds attached and sent it to him but he told me that he didnt receive any mails from me.
How can i know if my guildmate told me a lie?

thx for help

Ask your guildmate to delete some of his old mail. Not NPC mail, mail from other players- see if he gets it then. His box may be full.

Yeah, you can only hold 10 mail from players, after that it is considered full and it gives you no actual warning,