Strict Address Parsing

Information Details

Normally, the reason you have reached this page is because a mail server has sent you a message when it rejected an email from you, or one of your users.

  • If you are an email or network operator, you can continue reading this section
  • If you are a user sending email and it got blocked, you should read this section instead

Information for Email and Network Operators

Although email servers can by RFC accept connections that have a poorly formatted recipient address, most email servers and clients are configured to use standard conventions, and you should ensure that your systems also use these same standard conventions. Normally, this will not be triggered by most up to date email servers or email clients. However, some older automated reporting tools, or scripts may not have been designed in an RFC compliant manner.

This rule performs simple checks on the format of the MAIL FROM: contents. It checks to ensure that the MAIL FROM: is not empty, uses the more common format of <> vs just, and is a full email address in the form of

In order to ensure that messages are not stopped by this check, make sure the MAIL FROM: is in the standard RFC compliant form

The MAIL FROM: string sent should in the style of:



The following bad example(s) will get rejected:

MAIL FROM: <ellen>
MAIL FROM: <ellen@>

Spammers will often be caught by this rule, as they try to use sneaky MAIL FROM: and RCPT TO: commands to get by spam filters or deliver to mailboxes without knowing the full email address of the owner.

If you are the one sending the message, and you were blocked with this message, it is most likely that you do not have your email client set up correctly, and you should read the next section.

Information for users. Why was my email blocked?

If your email was blocked, and the link sent you here it is probably because either you mistyped or misspelled the email address, or your email provider does not have their email server configured correctly. Careful how you type email addresses.
Your email client and your outbound email server will normally deal with this correctly, however watch the typos. In your email client you should use To: or “My Friend” <> Also, make sure that you have in your account settings, the outbound SMTP settings correct, and no junk in the username section.

The main problem will usually be in your email/account settings, (eg. in Outlook or Thunderbird)

Make sure you are using SMTP authentication, or contact your ISP for more information.

Normally, this rule will only block spammers who run automated mailing software with forged addresses where the software is either not programmed correctly, or intentionally includes bad information to try and fool some forms of Spam Protection.

Please check that you use the correct method to connect to your ISP in your email client, or contact the administrator of your outbound email server, or ISP for more information.