SMTPSMIMEHandling1
Use this to specify whether to send outbound email if there are encryption and digital signing errors on the backup SMTP server.
Set to 0 (zero) to ignore S/MIME errors and send email in plain text if it can not be signed or encrypted. The errors are recorded in the SMTP log.
Set to 1 (one) to not send email if S/MIME errors occur. The default is 1.
See MultiChannel Framework: Configuring Signed and Encrypted Emails for additional configuration required for outbound emails with digital signatures.