Consider a board whose the board-wide emails are enabled (see Email settings at ACP), so that anyone can send email to the administrators, thanks to a dedicated contact page.

On that board, the forum permission « Can email topics » for a given user is set at "yes". Therefore, the option « Email topic » is visible in the topic tools for one or several forums.

However, if the user permission « Can send emails » is set at "no", he or she gets this error message when attempting to email a topic:

You are not permitted to send email to this user.

It doesn't make sense to display the option  « Email topic » if one cannot actually use it.

Either the option should be hidden when the user permission « Can send emails » is disabled, or people should be able to use the email topic feature as long as the forum permission « Can email topics » is enabled and regardless the user permission.