One of the main needs of a small business or startup is to have a reliable mail system with its own domain that helps differentiate on the Internet. Although there are lots of hosting plans offering free email accounts and even you could set up your own mail server, you are probably already used to mail services like GMail and would like to continue using it to also manage mail from your own domain without having to come to paid solutions such as G Suite (formerly Google Apps), which though inexpensive for the services you get in return, they represent an additional cost that your incipient project might not afford.
If this is your case you will be happy to know that thanks to the free tier offered by Amazon Web Services (AWS) in some of its services such as Amazon SES and Lambda, you can build a mail system at no cost that integrates seamlessly with your GMail free account, and at the same time allows you to send and receive mail from multiple mailboxes within your own domain.