---
title: "Understanding message failures"
date: "2015-03-20"
category: "email"
slug: "understanding-message-failures"
---

## Overview

When an outbound e-mail fails to deliver, the receiving server typically sends back a rejection notice explaining why. These notices are not standardized -- the format and language vary by provider.

## Anatomy of a Rejection Notice

A typical bounce message contains three parts:

1. **Modified subject line**: usually includes "Undelivered" or "Failure" (e.g., "Undelivered Mail Returned to Sender")
2. **Automated sender**: such as "Mail Delivery System", "Mailer-Daemon", or "postmaster"
3. **Failure reason**: embedded in the first few paragraphs of the message body

### Example Bounce Messages

**Sample 1:**

    This is the mail system at host sputnik.apnscp.com.

    I'm sorry to have to inform you that your message could not
    be delivered to one or more recipients. It's attached below.

    For further assistance, please send mail to postmaster.

    If you do so, please include this problem report. You can
    delete your own text from the attached returned message.

                       The mail system

    <shawn@host.ca>: host host.ca[100.200.3.4] said: **452 4.3.1 Insufficient system storage (in reply to MAIL FROM command)** 

**Sample 2:**

    Delivery has failed to these recipients or groups:
    Joe Blow (user@coca-cola.com)

    **Delivery not authorized, message refused**

    Your 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.

    For more information about this error see DSN code 5.7.1 in Exchange Online - Office 365.

**Sample 3:**

    Reporting-MTA: dns; apollo.apnscp.com
    X-Postfix-Queue-ID: 27CCC184D7D3
    X-Postfix-Sender: rfc822; myaddress@mydomain.com
    Arrival-Date: Wed, 18 Feb 2015 13:00:41 -0500 (EST)
    Final-Recipient: rfc822; user@example.com
    Original-Recipient: rfc822;user@example.com
    Action: failed
    Status: 5.4.4
    Diagnostic-Code: X-Postfix; **Host or domain name not found. Name service error** **for name=example.com type=A: Host not found**

## Common Rejection Types

### Invalid User

The recipient address does not exist -- likely a typo or the user has switched providers.

1. Sample:

    <test2@example.com>: host mail.example.com[64.22.68.20] said: 550 5.1.1
        <test2@example.com>: Recipient address rejected: **User unknown in virtual mailbox table** (in reply to RCPT TO command)

2. Sample:

    Subject: Some subject about cats
    Sent:    3/9/2015 11:09 AM
    The following recipient(s) cannot be reached:
       someuser@anotherdomain.com
       **The recipient has been deleted or has no e-mail address.**

3. Sample:

    <user@some.edu>: host mail.some.edu[100.200.150.250] said: 550 5.1.1
        <user@some.edu>... **User unknown** (in reply to RCPT TO command)

4. Sample:

    <someuser@gmail.com>: host aspmx.l.google.com[64.233.160.26] said: 550 5.2.1
        **The email account that you tried to reach is disabled**. wh8si1537215oeb.11 -
        gsmtp (in reply to RCPT TO command)

### Mailbox Full

The recipient's mailbox is at storage capacity and cannot accept new messages.

1. Sample:

    <shawn@oh.ca>: host oh.ca[7.2.5.37] said: 452 4.3.1 **Insufficient
        system storage** (in reply to MAIL FROM command)

### Misconfigured DNS

DNS maps domain names to IP addresses. If the recipient's DNS is misconfigured, the server cannot determine where to deliver the message.

1. Sample:

    <user@example.com>: **Host or domain name not found.** Name service error for name=example.com type=MX: Host not found, try again

2. Sample:

    Diagnostic-Code: X-Postfix; **Host or domain name not found**. Name service error for name=example.com type=A: Host not found

3. Sample (cannot connect to destination mail server):

    <guy@somedomain.com>: connect to
        somedomain.com[2.43.58.25]:25: **Connection refused**

### Misconfigured Greylisting

The recipient's server uses [greylisting](http://en.wikipedia.org/wiki/Greylisting) to temporarily reject e-mail as a spam reduction technique. The message is retried automatically within an hour, but misconfigured greylisting can cause delays of up to 8 hours per retry.

1. Sample:

    <user@example.com>: host mail13.mailrelay.com[216.119.106.129] said: **451 Greylisted, please try again in 300 seconds** (in reply to RCPT TO command)

### Relaying Denied

For mail to pass through a server, one of three conditions must be met: (1) the sender is [[unable-send-e-mail]] (authenticated) with the server via [[accessing-e-mail]], (2) the server is configured as the final destination for the recipient, or (3) the server is configured to relay to another server. If none apply, the message is rejected as an unauthorized relay.

1. Sample (recipient server misconfigured -- case #2):

    Reporting-MTA: dns; augend.apnscp.com 
    X-Postfix-Queue-ID: CA05A216020E 
    X-Postfix-Sender: rfc822; Arrival-Date: Fri, 2 Jan 2015 07:15:58 -0500 (EST) 
    Final-Recipient: rfc822; information@somedomain.com
    Original-Recipient: rfc822;information@somedomain.com
    Action: failed Status: 5.7.1 
    **Remote-MTA: dns; mx1.emailsrvr.com** 
    Diagnostic-Code: smtp; 550 5.7.1 <information@somedomain.com>: **Relay access denied.**

2. Sample (sender not authenticated -- case #1, resolve by [[unable-send-e-mail]]):

    The message could not be sent because one of the recipients was rejected by the server. 

    The 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.**', Port: 25, Secure(SSL): No, Server Error: 550, Error Number: 0x800CCC79

3. Sample (domain not authorized for mail -- case #2, resolve by [[authorizing-hostnames-handle-e-mail]]):

    Delivery to the following recipient failed permanently:
         info@mydomain.com
    Technical details of permanent failure: 
    Google 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].

    The error that the other server returned was:
    554 5.7.1 <info@mydomain.com>: **Relay access denied**

### DNS Blacklist

The sending mail server's IP has been added to a DNS blacklist, usually due to a compromised account sending spam. Open a support ticket in the [[logging-into-the-control-panel]] under **Help** > **Trouble Tickets** and include a copy of the bounce message.

1. Sample:

    550 5.2.1 Mailbox unavailable. **Your IP address 64.22.68.10 is blacklisted** using RBL-Plus. Details: http://www.mail-abuse.com/cgi-bin/lookup?64.22.68.10. (in reply to RCPT TO command)

2. Sample:

    Diagnostic-Code: smtp; 550 OU-002 (COL0-MC6-F14) Unfortunately, messages from 64.22.68.6 weren't sent. Please contact your Internet service provider **since part of their network is on our block list**. You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors.

3. Sample:

    Final-Recipient: rfc822; [recipient email address] Original-Recipient: rfc822; some@address.com Action: failed Status: 5.7.1 Remote-MTA: dns; mx241.emailfiltering.com Diagnostic-Code: smtp; 550 5.7.1 **Your IP 64.22.68.4 is blacklisted**. Click delist.emailfiltering.com to delist

4. Sample (broken heuristics on receiving side, not a true blacklist):

    Final-Recipient: rfc822; someuser@anotherdomain.com
    Original-Recipient: rfc822;someuser@anotherdomain.com
    Action: failed
    Status: 5.7.1
    Remote-MTA: dns; narya.dtnx.eu
    Diagnostic-Code: smtp; 554 5.7.1 Client host '64.22.68.65' rejected: **listed as**
     **suspicious, bad, or broken** --- http://dtnx.net/04/G/3M
