In researching Grouply, I found this link http://www.ncs-tech.org/?p=1146, which answered a lot of my questions about it.
The short version is that **In order for the service to work, you have to give them your Yahoo!ID and password.**
One you have given *anyone* those two bits of information, you no longer have personal control of your Yahoo account. *Anyone* with that information can change your email addresses, read any email in your Yahoo account, look at your private information in Yahoo’s registration — you get the idea.
To unsubscribe all your email accounts from their files, visit this link: http://www.grouply.com/unsubscribe.php
I’d suggest changing your Yahoo password (and any others you might have given to them) before that…
http://www.grouply.com/owner_controls.php is the group owner link to opt-out; I personally find “opt-out” requirements to be offensive – it should always be “opt-in”. There is also considerable discussion about Grouply on the Yahoo moderators groups, and there have been multiple requests for Yahoo to unilaterally opt-out or otherwise block Grouply.
You will get a confirmation code from Grouply at the group-owner address; input that into the opt-out form. Then go all the way down to the bottom and click on owner controls, you can opt out. This removes any messages from your list posted on their website, you can also keep members from posting invitations to your list from grouply by doing this. Both List owners and moderators can do it.
This is a public message, feel free to forward or link to as you desire.