I love this workflow and am using it for my Mail. Unfortunately I'm also using Thunderbird for other mail (had to switch because Mail was leaving too many processes open and my ISP was shutting down my site.) Seems to me I should be able to modify Vero's workflow to add Thunderbird but I'm having a hard time figuring out what the "file type" should be.
I think it is in ~library/thunderbird/Profiles/9olcaydl.default/ImapMail but all the folder in there have extensiosn like. msf and .sbd and I can drag them into the add box on the file types.
I'm in over my head. All I want is for Alf