Steps: 1. create a self signed pfx certificate RSA2048,SHA256 with CN and EMAIL fields for your e-mail address 2. import the certificate with gpgsm --import --cipher-algo RSA --digest-algo SHA256 3. make the certificate trusted with kleopatra 4. start claws mail and load smime and gpg modules 5. send yourself an encrypted e-mail with smime privacy 6. select the received message 7. the claws-mail will freeze My e-mail account was a gmail imap account. My OS is windows7 x64. Claws-mail is v3.9.1 as installed by the latest gpg4win. The signed e-mails works if they are not encrypted. GPG e-mails works. No customizations other than setting the gmail account and the default imap folders for claws-mail and importing self signed certificate were maid.
I enabled logs on gpg components and claws-mail doesn't generate any. The log of claws-mail looks normal.
I tested claws-mail in Debian 6 and in Windows. The version that came with Debian 6 is ok. The gpg4win version freezes at selection of any encrypted smime message. The certificate doesn't matter. It can send encrypted messages. The windows version from claws-mail works but gives a libintl-8.dll not found error.
it might be worth reporting it against gpg4win as well.