Response codes starting with number four mark a temporary problem.
422 The recipient’s mailbox has exceeded its storage limit or the size of the message exceeds the size limits for recipient’s incoming email.
431 Not enough space on the disk or an “out of memory” condition due to a file overload.
441 The recipient’s server is not responding.
444 The same as with 544 – transferring was (temporarily) unsuccessful, with 544 it’s permanently.
450 Requested action was not taken – The mailbox was unavailable at the remote end (possible reason – due to server maintenance server is offline).
471 Generic mail server error.
Response codes starting with number five mark a problem that concerns the recipient’s email address.
500 A syntax error: the server couldn’t recognize the command.
510 Bad email address.
511 The same as with 510 – bad email address.
512 A DNS error: the host server for the recipient’s domain name cannot be found – probably the email address is faulty or doesn’t exist.
521 Mailbox disabled.
522 The recipient’s mailbox has been full for a long time and probably the email address is abandoned.
523 The total size of your message exceeds the recipient server’s limits.
532 Server does not accept mail (probably because the recipient’s server is overloaded or due to server maintenance or the sender server’s bad reputation (e.g IronPort can set those restrictions)).
535 Server configuration error.
544 The message delivery was unsuccessful (probably due to an incorrectly set mailbox).
546 Looping problem. A contact has the same email address as an Active Directory user. One user is probably using an Alternate Recipient with the same email address as a contact.
550 Requested actions not taken as the mailbox is unavailable. The recipient email address does not exist.
571 Permissions problem. For some reason the sender is not allowed to email this account. Perhaps an anonymous user is trying to send mail to a distribution list.
Smaily specific codes
0 Subscriber hasn’t received any error codes.
200 Delivery successful.
1001 Subscriber unsubscribed in the latest campaign.
1002 Subscriber reported the latest campaign as spam. Is automatically unsubscribed.