SmarterMail 15.x Help
This documentation is for a product that is no longer supported by SmarterTools.

SMTP Blocking

The SMTP Blocked Sender list is an effective method for temporarily canceling a domain or indiviual user's ability to send email on the server. For example, if a particular account is sending an abnormal amount of email, you can add their address to Blocked Senders and they will be unable to send email until you remove them from the Blocked Senders list. Users and/or domains can be left on the list for whatever time you deem appropriate, and can be an effective stop-gap versus actually deleting the user and/or domain from the server.

To view blocked senders, click on the security icon. Then expand the Advanced Settings folder and click SMTP Blocked Senders in the navigation pane. A list of blocked senders will load in the content pane and the following options will be available from the content pane toolbar:

  • New - Adds a new SMTP blocked sender.
  • Edit - Edits the selected blocked sender.
  • Delete - Permanently removes the email or domain from the blocked senders list.

Adding a New SMTP Blocking Rule

To add a new SMTP blocking rule, simply click the New button. You are presented with the following options:

  • Block Type - Options are set as either Email Address or EHLO Domain.
    • Email Address - The complete email address to set up for the block.
    • EHLO Domain - This is the return value given when SmarterMail sends the EHLO or HELO command. A standard EHLO domain is the fully qualified domain name set up for the mail server you're wanting to block. (E.g., However, it IS possible that it will be something differnt based on whether the command is sent by the SmarterMail Web interface or an email client. For example, it may be the local IP address of the sending machine. Therefore, there is no well-established rule for what should be entered until some testing is done by the system administrator.
  • Blocked Address - Enter either the full email address or the EHLO Domain, based on the Block Type that was selected.
  • Direction - Specify whether to block either incoming SMTP, outgoing SMTP or both.
  • Description - Friendly description for the block.

NOTE: SMTP blocking does NOT occur immediately when the EHLO command is given. Instead, a "soft" block is used and SmarterMail will fail any authentication attempts or RCPT TO commands. This is because if the failure occurs right after the EHLO commaned, any person attempting to spam from a mail server could figure out what the problem is and change the domain given with the command on each send. A "soft" failure should, instead, make the spammer believe he is using an incorrect password.