Notification of new posts - without returning to Forum

[viaccess]

A couple of my users have asked if it's possible to receive an instant notification of all posts in a subscribed thread, even if they haven't returned to the Forums in the meantime. The problem is that they may read an 'I agree' post and ignore it, thereby not getting any further notifications, and missing a subsequent post that they would want to respond to.

So, is it possible to include a setting to allow a user to receive a notification of ALL posts, whether or not he/she has returned to the thread in the meantime? I understand why this may be inadvisable with very long threads, else the subscriber's mailbox would be spammed!

Sorry if this has been raised before, but I have looked and can't find it.

Thanks,

James