Can I stop D6's email sending to blocked users? I have a few actions. They send email to authors.
The problem is, I don't want emails to be sent if the user is blocked.

Any suggestion is appreciated.

ps: I couldn't create a tag on drupal.stackexchange.com . So tagging this custom-module for posting sake.
You could use hook_mail_alter() to check the mail before it's send and filter it depending on your conditions.