The specific implementation for BCC sends you an email entitled How To Make $TITLE Bingo Cards. Each subscriber to the list that I have a good guess for has a field in Mailchimp set with that value through their API. (Parsing the referrer is one option for guessing. My implementation is a mite more subtle, to avoid having user input there.)
The net effect is a few hundred people tomorrow who looked for [Halloween bingo cards] today and forgot about it will get an email tomorrow with the subject How To Make Halloween Bingo Cards. My open rates are "quite nice."
Edited to add: I got a note from the Mailchimp CS people back in April about having an unacceptably high unsubscribe rate (1.04% -- they take list quality seriously), paused my campaign to look into it, and forgot to unpause it. facepalm Thanks for prompting me to check on this (as usual, I don't look at things I think are working -- too much to do).
The net effect is a few hundred people tomorrow who looked for [Halloween bingo cards] today and forgot about it will get an email tomorrow with the subject How To Make Halloween Bingo Cards. My open rates are "quite nice."
Edited to add: I got a note from the Mailchimp CS people back in April about having an unacceptably high unsubscribe rate (1.04% -- they take list quality seriously), paused my campaign to look into it, and forgot to unpause it. facepalm Thanks for prompting me to check on this (as usual, I don't look at things I think are working -- too much to do).