This is a sample message you could use for a bouncing member:
Thank you for your post which is now on Freegle.
Your email address has been rejecting our messages. That means we have had more than 50 "soft" bounces from it (which means some kind of failure), or more than 3 "hard" bounces (maybe the address is invalid).
Please check the address we have in Freegle settings at https://www.ilovefreegle.org//where you will be able to SAVE to reset if it is correct, or amend if not.
This will enable you to receive any replies sent through our system.
Link: Sample Messages