Have you ever used the mass mail feature to re-promote your forum to those who have signed up and never really started posting, or was posting and then just suddenly stopped coming? It might not be "promoting" your forum on other sites, but it is promoting your forum to those who might have forgotten it.
I had it to where emails were sent out when an account didn't register a login for 3 months, however that's about it. It did help a little bit, re-promoting my forum, and out of that people starting coming back and posting more once they got that email.
I have done it a few times, and have had a number of members come back for a short time after doing that. I feel that the problem with why it wasn't successful with keeping them active, was an issue with the forum not being as active as it could have been, so they eventually went inactive again.
I have an article coming out about this soon on the Forum Promotion blog - stay tuned for that. But to sum up my basic point on this - mass mail generic 'we miss you' emails are not very effective, at least not for the majority. It lacks a personal touch and will often go unread. I suggest sending personalized emails to those who were previously considered active members, asking them how they are and not making it seem like a promotion to come back. Just check in with them and catch up with whats going on in their life - make yourself come across as a friend. It tends to be a lot more effective with those who were active members as they feel more valued. I did this recently on my forum for a member that hadn't visited in a month or so, and upon talking to them they made over 30 posts in one day.
I had a plugin that did that but I felt like it would bug members, even if only once a month. There was no unsubscribe feature in the plugin , and I'm pretty sure they always went to spam instead of people's inboxes which defeats the purpose. If the members aren't coming to your forum anymore at all, I feel that's it's going to take more than an email to get them back.
I don't think this method is very effective, people can easily ignore or delete the email if they find it annoying. I personally haven't tried this system before.
This kind of works, but nowhere near as much as you may have expected. Most people that stop visiting a forum do so for a reason, and not just because they forgot about it. In the end, I think you just end up bothering everyone.
Yes, yes, yes and yes. I always recommend this to forum owners. There's nothing worse than having inactive members. Some people simply forget about websites they visit. A friendly reminder of just how well your website is doing can't hurt anyone's inbox. Especially if you theme the email just right.
Add some images, whip up some HTML and make it look semi-professional, providing them with a reason to get back in the game. You never know, you may attract back just four members, but they may stick around and contribute a few thousand posts.