Sometimes an e-mail sent from the server to a recipient will fail. There are a variety of causes and as a “best practice”, the receiving side will report the failure reason for easy understanding. However, it is prudent to note that a reason is not mandatory (just good practice) and there is no consistent language through which these rejection reasons\u00a0are conveyed.<\/p>\n
A typical rejection e-mail\u00a0consists of 3 parts:<\/p>\n
This is the mail system at host sputnik.apnscp.com.\r\n\r\nI'm sorry to have to inform you that your message could not\r\nbe delivered to one or more recipients. It's attached below.\r\n\r\nFor further assistance, please send mail to postmaster.\r\n\r\nIf you do so, please include this problem report. You can\r\ndelete your own text from the attached returned message.\r\n\r\n The mail system\r\n\r\n<shawn@host.ca>: host host.ca[100.200.3.4] said: 452 4.3.1 Insufficient system storage (in reply to MAIL FROM command)\r\n<\/strong><\/pre>\n<\/div>\n<\/li>\n- Sample 2:\n
Delivery has failed to these recipients or groups:\r\nJoe Blow (user@coca-cola.com)\r\n\r\nDelivery not authorized, message refused<\/strong>\r\n\r\nYour message wasn't delivered due to an email rule restriction created by the recipient's organization email administrator. Please contact the recipient or the recipient's email administrator to remove the restriction.\r\n\r\nFor more information about this error see DSN code 5.7.1 in Exchange Online - Office 365.<\/pre>\n<\/li>\n- Sample 3:\n
Reporting-MTA: dns; apollo.apnscp.com\r\nX-Postfix-Queue-ID: 27CCC184D7D3\r\nX-Postfix-Sender: rfc822;\u00a0myaddress@mydomain.com\r\nArrival-Date: Wed, 18 Feb 2015 13:00:41 -0500 (EST)\r\nFinal-Recipient: rfc822; user@example.com\r\nOriginal-Recipient: rfc822;user@example.com\r\nAction: failed\r\nStatus: 5.4.4\r\nDiagnostic-Code: X-Postfix; Host or domain name not found. Name service error <\/strong>for name=example.com type=A: Host not found<\/strong><\/pre>\n<\/li>\n<\/ul>\n<\/li>\n<\/ol>\nRejection samples<\/h2>\n
This is not an exhaustive list, but instead a list\u00a0of common rejection notices that clients ask about.<\/p>\n
Invalid user<\/h3>\n
Explanation:<\/strong>\u00a0an invalid user is a user on the receiving side that no longer exists. This may be because of a typo in the e-mail address or the user has switched e-mail providers. Regardless, this address no longer exists (it’s like sending a letter to a defunct mailing address).<\/p>\n
\n
- Sample:\n
<test2@example.com>: host mail.example.com[64.22.68.20] said: 550 5.1.1\r\n <test2@example.com>: Recipient address rejected: User unknown in virtual mailbox table<\/strong> (in reply to RCPT TO command)<\/pre>\n<\/li>\n- Sample:\n
Subject: Some subject about cats\r\nSent:\u00a0\u00a0\u00a0\u00a03\/9\/2015 11:09 AM\r\nThe following recipient(s) cannot be reached:\r\n someuser@anotherdomain.com\r\n The recipient has been deleted or has no e-mail address.<\/strong><\/pre>\n<\/li>\n- Sample:\n
<user@some.edu>: host mail.some.edu[100.200.150.250] said: 550 5.1.1\r\n <user@some.edu>... User unknown<\/strong> (in reply to RCPT TO command)<\/pre>\n<\/li>\n- Sample:\n
<someuser@gmail.com>: host aspmx.l.google.com[64.233.160.26] said: 550 5.2.1\r\n The email account that you tried to reach is disabled<\/strong>. wh8si1537215oeb.11 -\r\n gsmtp (in reply to RCPT TO command)<\/pre>\n<\/li>\n<\/ol>\nMailbox full<\/h3>\n
Explanation:<\/strong>\u00a0the recipient’s mailbox is at its storage capacity and cannot receive any further e-mail until the recipient takes action to clean-up its\u00a0mailbox.<\/p>\n
\n
- Sample:\n
\n<shawn@oh.ca>: host oh.ca[7.2.5.37] said: 452 4.3.1 Insufficient\r\n system storage<\/strong> (in reply to MAIL FROM command)<\/pre>\n<\/div>\n<\/li>\n<\/ol>\nMisconfigured\u00a0DNS<\/h3>\n
Explanation:<\/strong>\u00a0DNS is what maps a domain name to an IP address and it is the IP address that a mail server connects to deliver a message. If\u00a0DNS is improperly configured on the receiving side, then the server can’t deduce where to deliver the e-mail.\u00a0As a concrete example: imagine delivering a letter to an individual’s house with an address; that’s DNS. Imagine delivering the message to the individual’s house, but you don’t know the address or don’t have the address available; the courier cannot deliver a message if he does not know the address to deliver. That’s what happens with a misconfigured DNS.<\/p>\n
\n
- Sample:\n
<user@example.com>: Host or domain name not found.<\/strong> Name service error for name=example.com type=MX: Host not found, try again<\/pre>\n<\/li>\n- Sample:\n
Diagnostic-Code: X-Postfix; Host or domain name not found<\/strong>. Name service error for name=example.com type=A: Host not found<\/pre>\n<\/li>\n- Sample (cannot connect to mail server at destination):\n
<guy@somedomain.com>: connect to\r\n somedomain.com[2.43.58.25]:25: Connection refused<\/strong><\/pre>\n<\/li>\n<\/ol>\nMisconfigured greylisting<\/h3>\n
Explanation:<\/strong>\u00a0the recipient’s mail server is using a greylisting<\/a> technique to reduce spam by temporarily<\/em>\u00a0rejecting e-mail. E-mail will automatically be retried within a hour, but if greylisting is improperly configured\u00a0on the recipient’s side, e-mail may exponentially delay up to 8 hours per retry. If greylisted entries are reset every 4-6 hours, then some e-mail may remain undeliverable.<\/p>\n
\n
- Sample:\n
<user@example.com>: host mail13.mailrelay.com[216.119.106.129] said: 451 Greylisted, please try again in 300 seconds<\/strong> (in reply to RCPT TO command)<\/pre>\n<\/li>\n<\/ol>\nRelaying denied<\/h3>\n
Explanation:<\/strong>\u00a0when mail passes through a server, one of three things must happen: (1) the client sending mail must be authenticated<\/a> with the server usually by sending a login\/password<\/a>, (2) the receiving server must be configured to know its the final destination for the recipient, or<\/em> (3) the receiving server must be configured to pass the message off to another server en route to its final destination. If any of these conditions are not met, it is construed as an unapproved\u00a0“relay”, which is case #3<\/em> without proper configuration.<\/p>\n
\n
- Sample (case #2, recipient end is improperly configured as reported by\u00a0Remote-MTA<\/em>):\n
Reporting-MTA: dns; augend.apnscp.com \r\nX-Postfix-Queue-ID: CA05A216020E \r\nX-Postfix-Sender: rfc822; Arrival-Date: Fri, 2 Jan 2015 07:15:58 -0500 (EST) \r\nFinal-Recipient: rfc822; information@somedomain.com\r\nOriginal-Recipient: rfc822;information@somedomain.com\r\nAction: failed Status: 5.7.1 \r\nRemote-MTA: dns; mx1.emailsrvr.com<\/strong> \r\nDiagnostic-Code: smtp; 550 5.7.1 <information@somedomain.com>: Relay access denied.<\/strong><\/pre>\n<\/li>\n- Sample (case #1, destination e-mail elsewhere, resolve by authenticating<\/a> with the mail server):\n
The message could not be sent because one of the recipients was rejected by the server. \r\n\r\nThe rejected e-mail address was 'user@anotherdomain.com'. Account: 'mail.mydomain.com', Server: 'mail.mydomain.com', Protocol: SMTP, Server Response: '550 5.7.1 <user@anotherdomain.com>... Relaying denied. Proper authentication required.<\/strong>', Port: 25, Secure(SSL): No, Server Error: 550, Error Number: 0x800CCC79<\/pre>\n<\/li>\n- Sample (case #2, if domain is part of your account,\u00a0resolve by authorizing server<\/a> to handle mail for\u00a0domain):\n
Delivery to the following recipient failed permanently:\r\n info@mydomain.com\r\nTechnical details of permanent failure: \r\nGoogle tried to deliver your message, but it was rejected by the server for the recipient domain mydomain.com by mail.mydomain.com. [64.22.68.62].<\/pre>\nThe error that the other server returned was:\r\n554 5.7.1 <info@mydomain.com>: Relay access denied<\/strong><\/pre>\n<\/li>\n<\/ol>\nDNS blacklist<\/h3>\n