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Sending Email Errors

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Overview

Our email servers may direct you to this page for more information regarding an error. Please see below for the message that matches the error you have.

Error Codes

Error codes, CA1, CA2, CA3 and BO are designed to help stop the spread of spam and 'backscatter' through our email servers. We do welcome feedback on this.

CA1

We reject the message with:

"Error CA1 see: http://wiki.aa.org.uk/Sending_Email_Errors John.Smith@example.com is blocked from sending. Probably a compromised account."

In most cases, we would also send an email to the customer with details of why the account has been blocked.

This suggests that you are sending email through smtp.aa.net.uk with authentication. but the system has detected a high amount of invalid email addresses that the account is sending email to, around 20 failed messages in an hour, however these figures are subject to change without notice. Feature added December 2013. There are 2 main reasons for this:

Possible Compromised Account?

The account may be compromised and a third party may be using your account to send lots of junk email. Typically a junk sender will send lots of emails and many will be to invalid addresses. To help prevent spam we have blocked the account from sending further email. Please contact support for more details, we would request you to change your email password before we unblock the account.

Sending to a Mailing list with invalid addresses?

It may be that the account has been blocked as you have a mailing list that you send email to that has many invalid email addresses. When you send email to invalid addresses you would get a bounce back message. It is normal practice to then remove these invalid email addresses from your databases. In this case, ask Support to unblock the account.

CA2

An IP address has been blocked from sending email through smtp.aa.net.uk due to the IP sending:

  • a number of high spam scoring messages in a short period of time, around 20 high spam scoring messages in an hour,
  • or, a high number of emails to invalid email addresses, around 20 failed messages in an hour,

(These figures are subject to change without notice.)

We reject the message with:

Error CA2 see: http://wiki.aa.org.uk/Sending_Email_Errors x.x.x.x is blocked from sending. Probably due to sending spam messages.

In most cases, we would also send an email to the customer with details of why the IP has been blocked. In many cases the IP is a third party unknown to the customer who has managed to obtain

CA3

A Mailbox has been blocked from sending email through smtp.aa.net.uk due to it sending a number of high spam scoring messages over a period of time, around 40 high spam scoring messages over a period of 6 hours, however these figures are subject to change without notice. The reason for the long time period is that it is known for compromised accounts to be sued to 'dribble' spam messages at low rates.

We reject the message with:

Error CA3 see: http://wiki.aa.org.uk/Sending_Email_Errors John.Smith@example.com is blocked from sending. Probably due a compromised account.

In most cases, we would also send an email to the customer with details of why the Mailbox has been blocked.

Possible Compromised Account?

The email account may be compromised and a third party may be using your account to send lots of junk email. Typically a junk sender will send lots of emails and will be scored highly by are spam checking software. To help prevent spam we have blocked the account from sending further email. Please contact support for more details, we would request you to change your email password before we unblock the account.

BO1

We reject the message with:

"Error BO1 see: http://wiki.aa.org.uk/Sending_Email_Errors#BO1  We don't allow sending of bounces due to backscatter problems. Contact Support if needed."

This means that we have blocked sending of a non-delivery report type message. This would be an email, typically from a customer server, that is a bounc eback message. Rather than rejecting the incoming message at SMTP time, the customer mail server has accepted the incoming message and then decided that it was now wanted, and generated a new email back to the original sender saying that the message has not been delivered.

We don't allow sending of bounces back messages due to backscatter problems. -i.e., most of the time the message being rejected is spam, and so a reply to the spam just means that email is being sent to an invalid address anyway. This can cause our servers to be placed on to blacklists, and it is better practice to reject email at smtp time.

In these cases, please configure your email server to reject mail at SMTP time, or to send messages by MX records rather than relaying through smtp.aa.net.uk.

We catch this by matching a null sender address, i.e. the sender email address is <>, and a list of known subject lines that are bounce back messages e.g.:

DELIVERY FAILURE
Delivery Notification: Delivery has failed
Delivery failure: Returned to Sender
Message you sent blocked by our bulk email filter
Delivery Status Notification
Mail System Error - Returned Mail
Mail delivery failed: returning message to sender
Returned mail: User unknown
Returned mail: see transcript for details
Undelivered Mail Returned to Sender
failure notice
Permanent Delivery Failure
Returned email
Transient Delivery Failure
There may be others...


Greylisting

You came here probably after seeing a mail of yours being rejected with a message like this:

Greylisted for 300 seconds 

The mail server generating this error message is using a system called Greylisting to filter spam and viruses. It relies on Mail Servers behaving according to the standards and usually doesn't require any action by the user. Your mails should only possibly be delayed.