- No command to make a new filter based on the current message. I used this all the time in Eudora to setup mailing list filters, and it's a pain to go back to manually enter filter parameters.
- No recipient list support. This is a Eudora shortcut where a set of addresses can be tagged to appear in a context menu where you can quickly send a mail to those people or forward on a message you've received.
- No redirect command. This is like forwarding a message, but it's resent with the original From: address and without any quoting. Your address is put in the Sender: header.
- No reply stationery. This is a Eudora feature I use a lot where you can reply with a prepared template. I usually use this to answer Palm OS programming questions with boilerplate instructions on how to get help through proper channels.
- The folder view didn't show a distinction between a folder that holds other folders and a folder that holds messages. I suppose this is because Thunderbird allows messages to be stored in any folder.
- The cursor is unresponsive, frequently staying in a "drag" or "busy" shape even after those operations are complete.
- No task window to show the progress of downloading and posting messages.
On the plus side, the importing of a gigabyte of mail into Thunderbird went well after I turned off virus checking, and all the messages I checked were imported correctly, including formatting and attachments. In the end, I'll continue to use Thunderbird for USENET and other news servers, but I'm sticking with Eudora to handle email for the near future.