Received a question asking “can email addresses be just a few characters?”
Many email providers limit how short or how long the email address can be.
As examples, Gmail (which provides addresses @gmail.com) rejects requested email addresses less than 6 characters to prevent spam. See https://support.google.com/mail/answer/7993
Microsoft (Outlook.com and “Hotmail.com”) addresses can contain only letters, numbers, periods (.), hyphens (-), and underscores (_).
No special characters, accented letters, or letters outside the Latin alphabet.
If you are setting up your own email server, or using Google Apps, you can pick what you want to be a valid email address. For example, at the TTCS, we can have email@example.com, or even !@ttcsweb.org if we choose.
As long as it complies with Internet rules, any email provider can make their email usernames however they want.