I recently got into Gmail‘s labelling system, which is pretty cool. You can create as many labels as you want, then label messages with as many of those labels as you want. Underneath the list of message folders, is a list of your labels, which you can click on to see a list of messages with that label (virtual folders).
Mozilla Thunderbird has similar functions, that can accomplish that, but with limitations. There’s the saved search folder feature which can not only achieve virtual folders for labelled messages, but for any search criteria. Then there is Thunderbird’s own labelling system, which works almost the same as Gmail, except 1)you have a limit of 5 labels, and 2)you can only apply one label to a message.
This is something I would love for Thunderbird to have; so I went through Bugzilla to search for any RFEs. I found Bug 114656 [allow arbitrary number of labels], and voted for it. Then I read comment #44, which points out an extension to help achieve this.
The Header Tools extension (by Audilecce) allows one to modify/add/remove headers of an email message. This means you can add your own header to a message, such as ‘X-Labels’ or ‘X-Categories’, and apply as many labels as you wish. You can set up saved search folders with the criteria [X-Labels][contains], and list the label. You can even have one saved search folder for a combination of labels.
Of course, I’d like each message to display its labels. This is where one of my favourites extensions can be used. Mnenhy is an extension that allows one to customize header views. These two are a match made in heaven!