Now that Google Apps closed sign-up for free plans, lots of people are looking for alternatives to Gmail for their own domains. Actually they don’t need to.
You can simply add other domains to your existing Google Apps account as separate domains to set up emails such as email@example.com. The separate domain emails perform exactly like those of the primary domain, with all the good stuff of Gmail, except you can’t do these things with a separate domain.
To add a separate domain to your existing Google Apps account, just login in the admin console and click “Domains” (click “More controls” if not visible) => click “Add a domain or a domain alias” => select “Add another domain” => enter the domain name => “Continue and verify domain ownership”.
After the routines of verifying ownership and setting up MX records, you can go ahead and add users / emails to the separate domain.
In most cases, you don’t need to find a Google Apps alternative this way, unless you hit the maximum number of users per account.