When we execute the SMTP command, we'll receive a reply from the mail server in the form of a three digit number followed by information describing the reply.
Please find the list of reply codes from the Server.
A system status or help reply.
The server is ready.
The server is ending the conversation.
The requested action was completed.
The specified user is not local, but the server will forward the mail message.
This is a reply to the DATA command. After getting this, start sending the body of the mail message, ending with "\r\n.\r\n."
The mail server will be shut down. Save the mail message and try again later.
The mailbox that you are trying to reach is busy. Wait a little while and try again.
The requested action was not done. Some error occurs in the mail server.
The requested action was not done. The mail server ran out of system storage.
The last command contained a syntax error or the command line was too long.
The parameters or arguments in the last command contained a syntax error.
The mail server has not implemented the last command.
The last command was sent out of sequence. For example, you might have sent DATA before sending RECV.
One of the parameters of the last command has not been implemented by the server.
The mailbox that you are trying to reach can't be found or you don't have access rights.
The specified user is not local; part of the text of the message will contain a forwarding address.
The mailbox that you are trying to reach has run out of space. Store the message and try again tomorrow or in a few days-after the user gets a chance to delete some messages.
The mail address that you specified was not syntactically correct.
The mail transaction has failed for unknown causes.