S/MIME signed mails showing unsigned


I am using SMIME Plugin
When sending signed messages in desktop- or webapp the message is correctly shown as signed in sent folder, but is shown unsignd in the inbox of the recipient. Same when sending signed messages to myself. In Outlook with ActiveSync without problems.

Encryption/Decryption works perfect in webapp!

Any idea?

Many thanks in advance!

Is the s/mime plugin enabled at the recipient side?