This is probably a bug in Thunderbird 91.5.0 (64-Bit) on Xubuntu 20.04: Wehen I double-click on an mail, which I have stored with TB, TB opens and asks me for my password. Then it opens the stored email (one, which I had sent recently, a non-encrypted signed one). But TB does not show the content of it but rather a box with: ''Dies ist eine verschlüsselte OpenPGP-Nachricht, aber Unterstützung für OpenPGP-Entschlüsselung ist nicht verfügbar.'' (decryption is not available) However, if I uses the same session of TB to open the *.eml-file in Question by the '''File>Open file''' dialogue, I can open it. '''BTW:''' Looking into this file with Geany, I see among other parts (including the plain text) 1. a block Content-Type: text/plain; charset=UTF-8; format=flowed, Content-Transfer-Encoding: base64 followed by base64-data (character garbage), 2. a PGP PUBLIC KEY BLOCK with by other character garbage, 3. my PGP Signature block with by other character garbage. Apparently all these parts are used meaningfully when I open the particular file through the '''File>Open file''' dialogue, except that the mail is not indicated as a signed one, which it most probably was since I always sign outgoing emails. That's probably another bug. When I double-click again on the same file in Thunar, while it already has been opened by TB showing the above mentioned error message, it opens correctly like above. However, if I open TB in the normal way, i.e. not by double-clicking on a stored email, I am first asked for my password (as expected). If I open the stored file then by '''File>Open file''' it shows the email as if I had opened it from the "sent" storage, i.e. with the symbol that it is a signed email and tools to show more about the applied key. I suppose this is a glicht which can be easily corrected by internally following the same sequence of events for the file after a double click on it in the Thunar file browser and then perform the same steps after the password dialogue ais if the file had been selected by a file open dialogue.