We had some issues with spam being sent through our server, we got IP blacklisted and a solution to the problem was provided from CBL. After the solution being implemented several websites werent able to send any messages.
The solution provided by CBL:
You will NOT be allowed to self-delist Darkmailer/DirectMailer CBL entries. You must fix the problem first.
We've heard rumors that the "SMTP Tweak in cPanel" doesn't work. But enabling CSF SMTP_BLOCK does.
You can find out more detail on this by doing google searches for "YellSOFT DirectMailer" or "DarkMailer", including screenshots of the control panel this software installs on your web server (the control panel in Russian).
See, for example, Darkmailer in Wikipedia and this thread in the CPanel Forum.
Note the references to "csf SMTP_BLOCK" and "WHM's SMTP Tweak"
The presented solution was to activate smtp_block but this blocks several websites that use php to send emails.
Any sugestion or advise to get a final solution that does not affect the service?