Can anyone help me rescue my mangled emails?

Question

Some time ago, I migrated to Apple Mail from Thunderbird using Mail's importer (on Leopard, I think). Unfortunately, it mangled some of my emails. I've since found that emails I thought were missing are actually still there, but stuck on the end of other emails. It's as if the importer couldn't find where to split some emails. Some of the resulting mailbox files are MBs big with many emails merged into one.
The only options I think I have open are:
1. Reimport the old Thunderbird data again using Eudora Mailbox Cleaner, then use duplicate detection to remove emails already imported. However, since I'm now running Lion and EMC won't run on Lion, I may run into compatibility issues.
2. Find some way to split the mangled emails. I've found where Mail keeps its files, but it looks like I'd need to figure out how Mail numbers the .emlx files and whether or not I need to update some database as well as splitting the files up.
If anybody reading this has any ideas or helpful info, I'll be forever grateful! :-)
Thanks,
Jon

Answer 1

Thanks, Tony. Yeah, it's those .emlx files I'm looking at. I managed to use csplit to split the combined emails into one file per email. However, when I rebuilt the mailbox, they just produced a bunch of empty emails. But I noticed a discrepancy in the headers:
This is valid:
211906
X-Account-Key: account5
X-UIDL: 5a1c0c4b2dbc61b59daf2f679de1d414
X-Mozilla-Status: 0201
X-Mozilla-Status2: 00000000
X-Mozilla-Keys:                                                                                 
Return-path: …
This "From - {date}" seems to be the cause of the mangled import:
From - Wed Feb 13 14:51:48 2008
X-Account-Key: account5
X-UIDL: 0bdd3d33043d2e403ca69d9eb0393d34
X-Mozilla-Status: 0211
X-Mozilla-Status2: 00000000
X-Mozilla-Keys:                                                                                 
Return-path: …
I'm not sure what the "211906" number is at the top of the valid email (some sort of ID maybe, but I can't find any documentation), but replacing the "From - {date}" with that number and then rebuilding the mailbox kind of works; I've ended up with working emails but the blank emails as well. So, I'm nearly there I think!