Thank you for your reply.
To take into account the number of posts I suggest the rule I'm manually using now i.e.
the message is sent if the number of days since last post divided by the number of post is greater than 10
that value (10) could be a parameter.
For instance (based on my forum www.leforumrecifal.com
Fredm has posted 10 messages, last visit on october 25 (146 days ago) : 146 / 10 = 14,6 => well message
kauderni has posted 17 messages, last visit on october 16 (155 days ago) : 155 / 17 = 9,1 => no message : even if his last visit is older than Fredm he has a bonus because he has posted more messages.
About the delay between messages, I understand the rule.
For my fourum I would like to set the delay to 6 month thus message if the user has not posted for 180 days.
He would thus receive the second message after a year, the third after a year and an half, ... it's too long !
I suggest an additionnal distinct parameter for the delay between messages
so I could set for instance the first message after 6 month and then an additionnal message every 30 days.
Thanks a lot for your attention