MX Guarddog is compatible with all SMTP servers, since all email communication on the Internet uses a standard protocol to communicate.
However there is one webhosting control panel - called vDeck - that does not support any 3rd party email security service such as MX Guarddog. They have their own integrated anti-spam service, if you attempt to use any 3rd party service they will immediately disable your email service.
If your hosting service uses vDeck you are not able to use MX Guarddog or any other 3rd party email security service at this time (as of Nov. 2013 and verified again August 2015).
If your website is hosted on a vDeck based server but you host your own email server at another location, perhaps MS Exchange at your office, then you can use MX Guarddog to protect your email.
If the email security solution your hosting company is providing you with vDeck is not adequate let them know that you want to use a service such as MX Guarddog and see if there is any way they will permit you to do so.
If they are not able to provide you with a method to use a 3rd party email-security you would need to switch to an alternate hosting company.