Mails bouncing from a particular mail id

Mails bouncing from a particular mail id

Hi , 

A friend of mine is using Thunderbird client and his hosting services , some how mail to his id at kesavan@impressivefirm.com from my zoho mail keeps boucing with error code 550.

His mail box is nor full and his mails to my gmail id works just fine. Kindly help me fix this .

Regards , 

Nirmal