b2evolution internally uses a unique function (send_mail()) through which ALL outgoing emails are piped. This function logs all emails it tries to send into this list. If an email does not appear here, b2evolution didn’t even try to send it.

By default all those emails are passed to the PHP mail() function. The status column will show whether the mail() function accepted them (green dot or black dot) or encountered an error (orange or red dot). If you get orange or red dots, see Emails don’t arrive / Email notifications don’t work.

In more recent versions of b2evolution, you can also configure an external SMTP gateway. In that case b2evolution will connect directly to that SMTP server instead of using the mail() function.

Finally, some users may be temporarily or permanently blocked and b2evolution will refuse to send them additional emails. This is to avoid behaving like a spammer. In that case b2evolution will display a red dot in the status column.