If the Microsoft Exchange Server has not enabled the client's "support S/MIME" option, the recipient cannot view the digital ID through their organization's Microsoft Exchange Server. To resolve the problem, use one or more of the following methods:
Method A: Follow these steps before sending a message:
1. On the File menu, click Properties.
2. On the Security tab, select Send clear text signed message.
Method B: Enable a default setting:
1. On the Tools menu, click Options.
2. On the Security tab, click Add digital signature to outgoing messages.
3. Select Send clear text signed message.