211	System status-
220	Service ready
221	Service closing transmission channel
250	Ok
251	User not local. Will forward
354	End with CRLF
421	Service not available. Closing connection
450	Item not found
451	Error in processing
452	Insufficient system storage
500	Syntax error, command unrecognized
501	Syntax error in parameters
503	Bad sequence of comands
550	Item not found. No access
551	User not local. Please try 
552	Exceeded storage allocation
553	Mailbox name not allowed
554	Transaction failed