The first step in making the guessing of the email server IP address fail is to make the email server and the web site server be on different IPs. HotDoodle sites by default place both on the same IP so one or the other has to be moved.
Technically, it is much easier to move a website than to move emails and the related user accounts and storage places. This is particularly true when one knows everything about the site, as we do with our websites. So if bypassing spam is a problem we move your website to another server.
Impact of the move:
If we control the name servers of the domains used with the site we can move the site without impact. The site will not be down even during the time it takes to propate the new DNS information. If the name servers are not ours, you can either share their login credentials, or can make the changes yourself.