Email client reports that email digital signature is "invalid". Some email software report a security problem with the email message because the digital signature is not valid. The email program may report the email message is tampered with. The email program may report the digital signature has been tampered with.
1. Open the email message in an editor.
2. Look for a Content-Type header with a protocol of application/x-pkcs7-signature. The following is an example:
Content-Type: multipart/signed; protocol="application/x-pkcs7-signature"; micalg=SHA1; boundary="----=_Part_119314_18824474.1291999242911"
1. Open the received email message processed by SMSMSE in an editor.
2. Look for the Content-Type and Content-Disposition headers in the body of the email. The following is an example:
Content-Type: text/html; charset="ISO-8859-1"
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
Notice the double quotes around the charset value. These were added by SMSMSE. The double quote characters are not present in the original message.
SMSMSE is changing the body of the email message with the addition of double quotes in the MIME section separators. This causes the digital signature to not match the body of the email message. Email programs then report the problem with the digital signature.
To prevent modification of the body of email messages during SMTP scanning, implement the following registry key: