How to block a user from sending emails

You may come to a situation where you want to block a user from sending emails. You don’t want to block the ability to check for emails, only the ability to sent emails.

DirectAdmin through SpamBlocker has 3 blocking files that you can use:

/etc/virtual/blacklist_usernames
/etc/virtual/blacklist_smtp_usernames
/etc/virtual/blacklist_script_usernames

Once the username is on /etc/virtual/blacklist_usernames, no emails can be sent – via SMTP or via a PHP script on the server. The user will be able to access the control panel, email accounts but will not be able to send emails.

– /etc/virtual/blacklist_usernames (does not need to exist). Must contain a DA Username, eg “fred” followed by the unix time it was added to the blacklist, eg: fred:1409557166 (may change it to be fred:1409557166:more=info&in=the&url=format, which won’t affect exim as it stops at the first : character) Will drop authorized smtp connections if DA User is in that file for the given smtp auth id (username or user@domain.com). Also applies to script based sends.. email will not make it into the queue, will be discarded and message logged to mainlog.

https://www.directadmin.com/features.php?id=1644

The command to use is:

echo "USERNAME:`date +%s`" >> /etc/virtual/blacklist_usernames

If the file doesn’t exist it will be created automatically by the above command. If you’ll try to send an email from the webmail, you will see a message like:

SMTP Error (550): Failed to add recipient “admin@plothost.com” (User account (plothost16) is not allowed to send emails. E-Mail delivery blocked.).

SMTP warning message

The same thing will happen if you are using an SMTP client like Microsoft Outlook or Mozilla Thunderbird:

The two other files that you can use (added in DirectAdmin SpamBlocker 4.4.6) are:

 /etc/virtual/blacklist_smtp_usernames – for blocking only SMTP access; the file allows the use of usernames or specific email addresses.

/etc/virtual/blacklist_script_usernames – for blocking only scripts by specific users; the file should contain the usernames.

DirectAdmin clarifies the addition of the two new blocking files:

 The SMTP/SCRIPT versions are used for specific items, while BLACKLIST_USERNAMES still blocks both, so you never need to add Users to more than 1 of the 3 files.

SpamBlocker changelog