It appears to have been a corrupted library somewhere within the system, went route of crash and burn as debugging didn't lead anywhere.
Complete removal and reinstall of all applications, and now I can attach files without a problem.
Thankfully, the system was running on a FreeBSD jail, and has heavy use of ZFS was able to rebuild system in a replica of the data set, in a test jail while production system was up and running minus the ability to email attachments.