Q: How do I make it so a disabled User can no longer access email and MRSware information? Since he is a remote salesman who has MRSware on his phone and computers.
A: To disable his MRSware login, go to "Users" in System Administration, right-click on his name and select "Disable". That both prevents login and removes it from billing.
If you are going to keep the Mailbox, but don't want him to login via phone/tablet, change the mailbox password.
Go to the Mailboxes list in System Administration, right-click on his mailbox and select "Set Password". It doesn't matter what you set it to since this is only for remote access, which you are effectively disabling by setting the password to something random.