If someone gave you feedback every 10 minutes, you would feel controlled.
If someone gave you feedback after every contribution, you would feel patronised.
A few principles here.
Feedback should never be predictable. Feedback should be random (in the eyes of the recipient). You shouldn't know if you're going to get feedback or not. That's part of what drives the contribution.
Feedback should never be in the form of gratitude. Feedback should demonstrate the impact the post made. Highlight the members it helped. Highlight the personal messages you've received stating what a valuable contribution it is with ideas to turn it into something bigger.
Feedback should never be too frequent or too sparse. For a heavy contributor, feedback works best between 2 to 4 weeks. For a lighter contributor, feedback every few months is better. Alternative, 1 in every 3 good contributions is a simple rule of thumb for delivering feedback.
This is also why you need a CRM system linked to the membership activity where volunteers can check who has / hasn't received positive feedback recently.