Some mails in various accounts aren't being displayed by Thunderbird. When selected the message frame just remains empty. The mail isn't marked as "read", but I can mark it via options as "read". "View message source" is working, "save Message to file" works, too. Moving the mail to another folder or repairing the folder won't make it being displayed. Reading the mail from another system with the same Thunderbird version (38.7.0, Linux x86_64) doesn't show this issue, so there seems to be something wrong in some settings. Common for all those messages is the Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; ...