I'm pondering the idea of importing a few thousand Thunderbird folders, each folder containing many emails of course, as a set of Emacs' Gnus mailgroups. Each mailgroup name would be derived from the folder hierarchy. Because of the quantity, the work is going to be fairly tedious, so I would automate this massive import if possible.
Among the available backends, nnfolder seems the most promising in this case. I presume it would be better to populate the mailgroups from within Gnus. Otherwise, I would have to thoroughly understand the nnfolder format, and this might require many iterations before I really get it right. Moreover, as email continues to flow in, iterations may become difficult to properly organize without loosing anything.
I guess I have to respool everything, under the constraint that the selected mailgroup is a function of the Thunderbird origin, overriding the standard Gnus selection mechanism. I did some Gnus coding in the past, but since I did not touch Emacs for a dozen years, it is all very rusty. I'm a bit lost about how to approach this task as efficiently and quickly as possible. So my question: how would you handle it? Or is there some clever Gnus hidden corner that I should explore more deeply? :-)
François
P.S. After I wrote this question, I found out that Gnus has a nice, helping function towards this goal. The idea is to first copy all Thunderbird folder files within the ~/Mail directory, as they are for the contents, but properly renamed. Once this done, M-x nnfolder-generate-active-file does at once, for each copied folder, edit the contents, leave a ~ backup, generate NOV data, create one mailgroup and, of course, adjust the ~/Mail/active file.
To copy the folders underneath the ~/.thunderbird/LOGIN/Mail/Local Folders/ directory, I wrote a small Python script. It ignores all .msf files, and recurse within .sbd directories. The folder path name, relative to Local Folders/, has all its .sbd/ strings turned into periods to produce the mailgroup name, also lowering case, turning spaces and underlines to dashes, and handling other special characters appropriately. In particular, non-ASCII characters are not handled properly, nnfolder is confusing UTF-8 and ISO-8859-1 here and there. The script also has to skip msgfilterrules.dat and likely drafts, junk and such things.
I notice two details requiring attention :
- Thunderbird itself can be used to compact folders before copying them, otherwise one might unwillingly recover messages which were already deleted.
(setq nnmail-use-long-file-names t)is needed in~/.emacsprior to the whole operation.
The batch transformation aborted, saying it is not able to decrypt one of the message. I moved the offending folder out of the way, and then, the lengthy operation succeeded.