How to implement a white-list-based system in Gmail?

Question

Is there a way to implement a whitelist-based system in Gmail? Specifically:

1. all messages coming from addresses in a "white list" get through;
2. all messages coming that are responses in a pre-existing thread get through;
3. all messages that include a special "passcode" string get through;
4. the remaining messages trigger an automated canned response giving instructions on how to get added to the whitelist; these massages are automatically marked as spam.

Thanks!

Answer 1

Enter the following in the search bar, replacing the angle-bracket delimited stuff with actual details.

-from:{<space-separated list of whitelisted emails>} AND -body:{<passcode>} AND -label:{whitethread}

Run the search, then click the dropdown arrow in the search box:

Select "Create filter with this search", and make it send the canned response.

Now, run a search for

from:{<space-separated list of whitelisted emails>} OR body:{<passcode>}

and make it apply the label "whitethread" in the same manner.

Also apply "whitethread" to all the emails in your account. (All Mails>Select All)

This will put all "whitelisted" emails/threads in a label, and check for mails:

which do NOT come from your whitelisted email, AND don't have the passcode, AND aren't in the whitelisted thread. Probably what you wanted :)