Often, shared hosting boasts unlimited disk space, unlimited bandwidth, unlimited domains, and basically unlimited everything. While they claim to offer unlimited resources, you’re required to be fully compliant with your hosting company’s Terms of Service and only utilize disk space and bandwidth in the normal operation of a personal or small business website.
That said, not all web hosts offer email. WP Engine, for example, does not. In such instances, you must email accounts from a company other than your web host. GoDaddy, for instance, sells email packages starting at $3.49 per user, per month. That might sound like a hassle, and just one more thing to keep track of, but there are actually some webmasters who feel that separating your email hosting and web hosting services is smart. That way, one provider going offline won't completely bork your business.
One thing we learned in reviewing the services listed here (and many more) is that even though the packages are very similar, they are not identical. Some are more security-focused than others, offering anti-spam and anti-malware tools. Others offer a variety of email marketing tools. While most of the hosts we've reviewed have built-in e-commerce, you may want to consider using a more-robust third-party online shopping cart application like Shopify instead.