The error itself looks like this:
To verify the email signature, navigate to System Maintenance > System Control Maintenance > User Control > User Control 1. Enter the User ID for the person who is getting the email error. Arrow down 4 lines to the Email Signature Maintenance window. Double check the email signature is free of any special characters. If special characters are present, they should be deleted or replaced with standard characters. You can then test sending the email again to see if it's successful. If the error persists, you may contact support@rmaster.com for further assistance.
Note: If your entire company has the same email signature containing special characters, you'll need to verify / edit the email signature for all Users as it applies.