[Andreas]

Here is a script I use on my board, maybe it is useful for you too.
What it does:
Users that hav max. x PMs, are in Group a, b or c, have never posted and were not axtive for the time y will get an email that they will be deleted after time z when they don't visit again.
After time z they will be deleted if they had not visited again and will get another email that they have been deleted.

1) Run the following query
[sql]ALTER TABLE user ADD inactivitytag INT ( 10 ) DEFAULT '0' NOT NULL;[/sql]
If you are using a table prefix put it in front of user
2) Edit inactiveusers.php to suits your needs (affected grouips, etc.)
3) Create the phrases userdelnotification and inactivitywarning in phrasegroups eMail Subject Text and eMail Body Text
4) Create a Cron-Job for inactiveusers.text to run once every day.

You can alos take a look here:
https://vborg.vbsupport.ru/showthread.php?t=75740
https://vborg.vbsupport.ru/showthread.php?t=78952

@lowandloudinc
This might work for smaller boards, but not if you get 100+ registrations/day
Doing so would only create tons of "Hi"-Posts, but then the users would'n post anymore.
At least this happend to me