I can confirm this for mails sent by Thunderbird users. After decrypting, I can save the "attachment.dat" locally and open it with a text editor, as Luigi described it. So it seems to be no problem of decrypting, but one of displaying.
But additionally, there seems to be a problem with verifying the signature of such messages: After decrypting, Evolution shows the message only as encrypted, but not as signed (Button on the bottom of the message). But when decrypting the message directly with gpg, it says: "gpg: Good signature from ...". So the message is actually encrypted and signed, but Evolution doesn't handle the signature.
I can confirm this for mails sent by Thunderbird users. After decrypting, I can save the "attachment.dat" locally and open it with a text editor, as Luigi described it. So it seems to be no problem of decrypting, but one of displaying.
But additionally, there seems to be a problem with verifying the signature of such messages: After decrypting, Evolution shows the message only as encrypted, but not as signed (Button on the bottom of the message). But when decrypting the message directly with gpg, it says: "gpg: Good signature from ...". So the message is actually encrypted and signed, but Evolution doesn't handle the signature.