An email signing certificate alone will not prevent your emails from being marked as spam. However, it can help in establishing trust and authenticity with the recipient's email server, which can in turn reduce the chances of your emails being marked as spam. This is because an email signing certificate confirms that the email has not been tampered with during transmission and that it has indeed been sent by the claimed sender. So, while an email signing certificate does not directly prevent spam, it can help in ensuring that legitimate emails are delivered to the recipient's inbox instead of getting caught in the spam folder.