To keep things simple, I want to organize my life as much as possible. For example, I teach at the college level and have a folder (named FPC) for messages from the college (students mostly, but occasionally other faculty and staff). That way, I can easily find college-related messages and they don't get lost in my Inbox.
I can drag and drop messages I want to have moved into the FPC folder, but a better solution is to have Thunderbird do this automatically. The tool for automatically processing a message is called a filter. Most email programs support filters, and Thunderbird is no exception.
A filter starts by looking at the message's header and body fields. The filter tests the values found with your test value. For example, I would check the Sender field to see whether it contains the text fpc.edu. If the text is found, it is a message from someone at the college and I can move it to the FPC folder. The header fields that Thunderbird checks are
Subject The message's subject field
Sender The name and email address of the sender
Body The actual message body text (this is significant only if you are fetching both headers and body text)
Date The message's date stamp
Priority The message priority, which can be set by the sender
Status The message status (junk or not junk)
To The specified recipient of the message (which might not be you)
CC The courtesy copy list
To or CC The To and CC fields, which are both tested
Age in Days Messages that are older than the specified number of days
Thunderbird's filters enable you to do more than just move a message to another folder, however. Filters support the following actions:
Move to folder Tells Thunderbird to move the message to the specified folder. Messages can be moved between different accounts. When a message is moved, it is removed from the Inbox and placed in the destination folder.
Copy to folder Enables you to create a copy of the message and move that copy to another folder. The original message is unaltered and remains in the Inbox.
There are more header fields than those shown in this list, and Thunderbird allows you to create custom header tests for your filters if you want.
Label the message Used with the message labels, described previously in the section "Labeling Messages."
Change the priority to Sets the message's priority to one of the five priority values: Highest, High, Normal, Low, and Lowest.
Set Junk Status to Flags the message as either Junk or Not Junk.
Mark the message as read Sets the message's status to read (even though you might not have read the message). If the sender has asked for a read receipt, this request is processed as part of this action.
Flag the message Sets the message flag.
Delete the message Deletes the message, sending it to the trash folder.
Delete from POP server If you have left the message on the POP server, delete it there. This does not affect the local copy of the message, if one exists.
Fetch body from POP server Tells Thunderbird to get the message's body from the email server. This option is significant only if you have set Thunderbird to retrieve headers and not message bodies.
Forward Message to With this option Thunderbird forwards any messages that match the filter's criteria. You specify the email address to which to forward the messages. The only problem with this feature is that you cannot add any body text to the message.
To match all incoming messages for an out-of-office response, simply define a rule that specifies that the subject not contain a long string of random characters. Because no emails will have those random characters in the subject, all will be processed by the Reply with Template function.
Reply with Template Most users utilize this as an out-of-office message. However, sometime you might want a standard response sent to the sender of the message.
Ignore thread Tells Thunderbird to ignore the entire newsgroup message thread; threads are defined as the thread's initial message and all replies to the message.
Watch thread Tells Thunderbird that this newsgroup thread is important and that it should track the thread.
With filters, the actions are not exclusive. You can choose one or more actions (such as Move to folder, Mark the message as read, and Change the priority).
To create a message filter, do the following:
In Thunderbird's Tools menu, select Message Filters.
In the Message Filters dialog box, click the New button.
In Filter Rules, name and create your filter.
Click OK to close Filter Rules, and then click OK again to close Message Filters.
Creating a filter is probably easier done than said, and after you create your first filter, the next one will be easier.
When using filters, you should check to see that the filter is doing what you expect at least for the first few times the filter is used.
For my email, I use about 15 filters. These filters look at subjects, senders, who the message is being sent to, and other information. Then most messages are moved to folders based on the results of these tests. Some messages are deleted, although that is an action that must be used carefully so as not to lose any important messages. (I usually delete messages that contain sexual terms; drug names; or words such as mortgage, loan, free, opt-out, and a few other words or phrases I have found to be common in spam.)
Each filter is applied in order, so a message processed with an earlier filter might not necessarily be processed with a later filter for example, when the earlier filter deletes the message.
After you have filtered your messages, you can organize them, too. Sorting and grouping are valuable tools.