As part of my work involves InfoSec I have some experience:
1.Problem has No connection to what browser or email client you use.
2. A robot web crawler visiting the site and not a member can see the adresses in every quoted reply
eg On Sat, Jun 19, 2021 at 6:10 AM Colin Herbert via groups.io <colingherbert=
3. The privacy and other setting of the groups user control page has no option to hide any email address in a message or quoted reply.
4. Once your address appears, only a matter of time before its sold with millions of other adresses to the spammers.
5. The solution is not with responsibility of group members but for the admin and Groups.io to fix the security gaps that permit complete email adresses to be publicly seen.
6. The Groups.io admin can find may other groups that have fixed this issue.