On two different Linux Mint 18.0 boxes, using TB 45.5.1 - I am able to attach eml files to outgoing mail and double click these to open in TB on one box, but doing the same thing on the second box, I am not able to. In more detail: Save selected email to desktop (or somewhere convenient) Attach eml file to an outgoing email message. Double-click attachment. (Preferred behavior - possible in the first box only) Attachment opens as a new TB email. I can review this opened email. I can close this and send off email. Problem: Unable to do this in the second box with exactly same OS and TB version Please help resolve this so that this option can work in both boxes Thanks