Email firewall, as the name implies, sits between the Internet and your corporate email server. It does not matter which vendor you use as your primary email server; as long as your email server accepts email using SMTP protocol, you can use Xeams to filter messages.
Benefits of using Xeams as email firewall
Works with any email server, including by not limited to:
And any other SMTP server
Nothing to install on your actual email server.
Blocks 99% of junk messages before they get into your network if installed in a DMZ