The first thing I'll say is that there are some features that Eudora Pro has that Thunderbird does not. But I simply decided that I'm willing to do without, and willing to wait for Thunderbird to catch up. Also, here are some numbers so you're familiar with my setup:

I have 485 mailboxes, 614 filters, about 100,000 e-mail messages. I migrated from Eudora v6.2.1.2 to Thunderbird v1.0.2.

Here are some issues:

Attachments

Thunderbird keeps attachments embedded in each e-mail message. There is no facility for automatically saving them in their own folder (which I liked because Norton AntiVirus would automatically delete any attachments that contained viruses). Note that if you go to Tools -> Options, there is an icon for Attachments, which includes a setting to define the folder to save them to. This does not work. See more info about this in the Mozilla Knowledge Base.

Filters

Thunderbird doesn't have anywhere near all the filter options as Eudora. A couple that I'm now doing without:

• speak the subject line and the sender's name of incoming messages
• play a wav file when certain e-mails arrive
• run an external program, passing the subject line to that program

Thunderbird provides the ability to import three things from Eudora: Address Books, Mail and Settings. None of these include filters. So all filters need to be re-created manually.

See also some issues about filters under the "Multiple Mail Accounts" heading below.

Importing Mail

When you import mail, Thunderbird does quite well. It took about 2 hours to import all of my 100,000 messages. HOWEVER, Thunderbird does not import the status of all mail. So, every message appeared as a new unread message. This was not good.

Some tips on this subject about this are available in the Mozilla Knowledge Base. There is a mention of a third party program called Eudora Rescue that will convert Eudora's mailbox files to a more standard format. The newly formatted mailbox files can then be imported into Thunderbird, and all statuses will remain in tact.

In my case, I had already done the import, and not wanting to wait another 2 hours to do another import (plus whatever time it would take to run Eudora Rescue), I decided to manually mark all my messages read. I did this by right clicking on every e-mail folder in Thunderbird and selecting "Mark Folder Read".

Junk Mail Filtering

Thunderbird has built-in junk mail filtering, just like Eudora. I have not been using it enough though to compare it. The features look very similar though.

Mailboxes

Eudora has the concept of having many mailboxes that can be organized into a folder structure. Thunderbird has the same, though everything is a folder. Also, in Thunderbird, you cannot create a new folder while moving a message into it (in Eudora, when you move a message to a different mailbox, you can select "New..." and create that mailbox on the fly). You must first navigate the folder structure, create the new folder, then go to the message and move it into that new folder.

Multiple Mail Accounts

I have 4 POP accounts that I check. In Eudora, all incoming e-mail goes into a single common In Box, then gets moved around based on all my filters. This is not so graceful in Thunderbird. Each account has its own Inbox. However, the Mozilla Knowledge Base has information on how to make all mail go to a Global Inbox.

Also, filters can only be created per POP account. A single filter cannot be automatically run on mail downloaded from multiple POP accounts, even if you're using a Global Inbox. The Mozilla Knowledge Base does provide a tip for handling this though. Since the filters are created in a single text file, you can simply copy that file to the folder for your other accounts. I created a batch file to do this.

Plain Text Messages (no HTML)

The marriage between e-mail and HTML should never have happened. But some folks like it, so Thunderbird comes configured to use HTML e-mail. The Mozilla Knowledge Base has a document explaining how to set Thunderbird to use plain text e-mail.

Signatures

Thunderbird does not have a function to maintain signatures, though you can attach a signature. So, you have to create your own signatures in simple text files (or HTML files), then define your signatures to be used in each account's settings. More info is available in this Knowledge Base document.