Some customers are getting warning messages about delayed or undeliverable email. Here’s a short explanation of what is happening.

Example

Here’s an example message sent by one of my customers. Info in {} brackets have been deleted to protect the identity of the message.

Subject: Warning: message 1X4uTU-0001z5-E3 delayed 48 hours

This message was created automatically by mail delivery software.
A message that you sent has not yet been delivered to one or more of its recipients after more than 48 hours on the queue on {mail server}.

The message identifier is:     1X4uTU-0001z5-E3
The date of the message is:    9 Jul 2014 12:12:03 -0400
The subject of the message is: {Original subject of the message}

The address to which the message has not yet been delivered is: {target email address} (ultimately generated from {another target address})

Delay reason: SMTP error from remote mail server after end of data:
host alt4.gmail-smtp-in.l.google.com [{IP address}]: [{IP address}] Our system has detected an unusual rate of unsolicited mail originating
from your IP address. To protect our users from spam, mail sent from your IP
address has been temporarily rate limited.

Please visit  http://www.google.com/mail/help/bulk_mail.html to review our Bulk
Email Senders Guidelines.

No action is required on your part. Delivery attempts will continue for
some time, and this warning may be repeated at intervals if the message
remains undelivered. Eventually the mail delivery software will give up,
and when that happens, the message will be returned to you.

 What’s happening

The mail server that is receiving the email, in this case a Google server receiving a gmail address, is complaining that your message might be spam. There is an “unusual rate of unsolicited mail originating from your IP address”.

But you are not a spammer, right! Why is it complaining.

You are probably using a shared server to host your email. You are sharing that server with many other customers. If somebody on the shared server has sent a bunch of spam, the IP address of that server might have gotten onto a black list or gray list. That means you, and other users of that shared server, are all judged to be potential spammers.

What can you do?

Unfortunately, there’s not much you can do to get a quick resolution. Possible next steps include:

• Be patient and wait for it to clear up on its own. Notice that “Delivery attempts will continue…”
• Submit a ticket to your hosting provider’s support line with a copy of the email. Tell them that you’re not responsible for any spam. The hosting provider will attempt to identify who the offending user(s) might be, stop the spamming, and then get their IP address removed from the black lists.
• Send your email by way of a different mail server. You would need a separate account with a different hosting provider to make this work.

More info

Some mail servers are more diligent than others about trying to detect spam. Recent changes at Google have made gmail addresses more sensitive to potential spam. That’s good for gmail users, but bad if you’re trying to send an important email to a gmail address.

Often, the offending user on the shared host is not really a spammer. More likely, their hosting account was hacked by somebody who then used the account to send a bunch of spam. Moral of this story: Use strong passwords on your hosting accounts so you don’t get hacked.