Administrative prohibition

Hey people.
I keep getting this error all the time


The server response was: Administrative prohibition

Use the pop-up menu below to try a different outgoing mail server. All messages will use this server until you quit Mail or change your network settings.

Message from: Nathaniel@logikstudios.co.uk <nathaniel@logikstudios.co.uk>


. sometimes my mail will work other times it wont can you please help me