Error message when using distribution list

I have been receiving the following error message when trying to send an email using a distribution list. What does it mean and how can I fix it?08:40:41 MailClient.Storage.Application.ItemOperationException: Cannot send message (Email body not accepted due to the following reason: 08:40:41 "5.3.4 552 5.3.4 Header size exceeds fixed maximum size

Hello Musotech,

How big is your distribution list? This unfortunately looks like the message is too big and the server refuses to accept it.