I've consolidated my address books and uploaded them to Thunderbird. One of the fields I've used is a tag' field which tells me what kind of contact they are, school, college, company etc. I'd like to search for a list of all school contacts for example. I'd then like to save that as a mailing list. Is it possible to do that without putting together a mailing list manually.

When I try and search I don't get the option to chose the custom field, just the basic name and address fields.