When exporting a sent mail folder in mbox format Claws includes it's own metadata headers which are not part of the mbix format and cannot be properly imported by other mail readers. Example: AF: NF:0 PS:10 SRH:1 SFN: DSR: MID: CFG: PT:0 S:myaddress@example.com RQ: SSV:sendingserver.com NSV: SSH: R:<receiver@example.com> MAID:6 In my particular case Thunderbird interpretd S: as the subject header and all my imported sent messages are listed with my own email adress as the subject line..
Although I agree that Claws Mail should not export its own 'special headers' when exporting to MBOX, there is, afaik, nothing in the MBOX specification which says that is not allowed. A bigger problem is with thunderbird conflating S: into Subject:. This is the real bug here. (I read on the mozilla pages that this bug was reported some years ago, and only effects the mailbox overview and not its message view.) I'll leave this open with regard to the first paragraph above.
fixed in git. thanks for the report.
*** Bug 4309 has been marked as a duplicate of this bug. ***