Switching between mail servers or hosting providers is pretty straight forward.  Here are some tips to ensure a smooth transition:

• Be sure that the MX records for your domain are always pointing to the hosts assigned by SpamHero. Doing so will ensure emails can be re-delivered if something goes wrong during the transistion. You can look up the correct MX records from within the SpamHero control panel by going to Settings > Mail Host (scroll to the bottom of the page).
   
• If your domain will also be using new name servers, setup your MX records before switching your domain to use them.  This is an important step to ensure that the MX records for your domain are always pointing the SpamHero service. 
   
• Ensure that you have setup all of your email addresses on your new mail server (or in your new hosting provider's control panel)
   
• If you're moving to a new hosting provider, check here for special instructions:
  Hosting Providers Requiring Special Attention
   
  Also, see this document as it applies to most hosting providers:
  Configuring cPanel with SpamHero
     
• Optionally secure your mail server to prevent spam from getting around the filter.  If you're changing hosting providers and you don't have a dedicated server then this step will not apply to you.  However, if you keep your MX records pointing to SpamHero through out the transition then it mostly eliminates the need for this step (spammers won't be able to cache your mail host IP if it's never published in your DNS).
   
• Optionally turn off your old mail server (or setup a firewall to drop inbound mail connections) so that mail defers.  Deferred mail will automatically be queued for delivery to your new mail host once it is online.
   
• When you're ready to change your mail delivery to your new mail host, login to your SpamHero control panel and go to Settings > Mail Host. Or, if your delivery mail host name will be staying the same (e.g. you're just changing the IP of your mail host) then you can force SpamHero to grab your new mail host IP by doing a Flush Mail Queue.  This can be done from within the SpamHero control panel by going to Tools > Flush Mail Queue and clicking on the Continue button.  This will also force all deferred mail to immediately deliver to your new host.
   
• After changing your mail host in the SpamHero control panel, send a test message from a server that's unrelated to the domain that you're moving (free email providers such as HotMail are good for this test).  Sending a test message from the same domain that's moving is discouraged because in most cases those messages are delivered without ever passing through the SpamHero service.
   
• If mail is not delivering to the new mail host you can check the mail delivery logs to see where the mail is going and what errors are occurring, if any.

What if something goes wrong?

As long as your MX records stay pointing to the SpamHero assigned hosts through-out the transition process, you can always re-deliver you email as instructed here:

View and redeliver clean messages