concretesubmarine.com/ FORUM

This is an error that occurs when trying to send an email that has been digitally signed without a valid internet certificate. To resolve it, users need to verify the certificates installed via the User Security settings and obtain a certificate from their administrator or a trusted CA if one is not available. If certificate problems hinder access to emails, eSoftTools NSF to PST Converter can export emails to Outlook while maintaining the integrity of signed emails so that access to vital communications is not disrupted.

More Detail - Your current ID does not specify an Internet certificate for signing