We are offering a few inboxes that will automatically respond with pre-defined error codes so that developers can more thoroughly test their implemenation with MailerSend (webhooks, etc.). The emails sent will count towards quota, but the results from said inboxes are not added to deliverability scores for accounts using them.
|Email Address||SMTP Error Code||Reason|
|email@example.com||550||User's mailbox was unavailable (such as not found)|
|firstname.lastname@example.org||421||The service is not available and the connection will be closed.|
|email@example.com||554||The transaction has failed (or you're not allowed to send to this recipient).|
|firstname.lastname@example.org||450||Requested mail action not taken: mailbox unavailable (e.g., mailbox busy or temporarily blocked for policy reasons).|
|email@example.com||450||Requested mail action not taken: DNS error|
|firstname.lastname@example.org||550||A DMARC policy issue. The recipient server did not accept our requests to connect.|