Parts of an Email Address and the Characters You Can Use in Them

Learn which characters you can use

@ sign made of puzzle pieces on white background

Horia Varlan / Flickr /  CC BY 2.0 license

Email addresses encompass several elements. Most prominent is the "at" sign (@) in the middle of every address. Before that comes the username, and after that comes the domain name. In this guide, we'll explain what username and domain names are, and what symbols you can use in an email address.

What Is an Email Username?

The username identifies a specific person or address in a domain. Whoever sets up your email address (you, your school, or your employer) selects the username. When you sign up for a free email account, for example, you can pick a creative username of your own.

Usernames used in a professional capacity usually employ a standardized format. For example, a company might use your first name, such as Bill@example.com. This is friendly and easy to remember. It also affords you some anonymity by not exposing your last name.

Here are a few other professional username options you might encounter:

  • Your first name and last initial, such as BillJ@example.com.
  • Your first initial plus your last name, such as BJones@example.com.
  • Your first and last name together, such as BillJones@example.com.

What Is an Email Domain Name?

Domains on the internet follow a hierarchical system. A certain number of top-level domains (.com, .org, .info, .de, etc.) exist, and these make up the last part of every domain name. Within each top-level domain, custom names are assigned to people and organizations applying for them. The domain owner can then set up sub-level domains freely, to form a name like bob.example.com.

Unless you buy your own domain, you don't have much say over the domain name part of your email address. So, if you create a Gmail address, you have no choice but to use gmail.com as your domain name.

Which Characters Are Allowed in Email Addresses?

The relevant internet standard document, RFC 2822, lays out which characters can be used in an email address.

In the standard's parlance, the username in an email consists of words, separated by dots. A word in an email address is called an "atom" or quoted string. An atom is a sequence of ASCII characters from 33 to 126, with 0 to 31 and 127 being control characters, and 32 being whitespace.

A quoted string begins and ends with a quotation mark ("). Any ASCII character from 0 to 177 excluding the quote itself and the carriage return can be placed between the quotes.

Backslash characters can also be used in email addresses, but they perform a different function. The backslash quotes any character and causes the following character to lose the special meaning it usually has in the context. For example, to include a quotation character in an email address, place a backslash in front of the quotation character.

You can use any ASCII alphanumeric character in your email address, as well as any characters between ASCII 33 and 47. Characters that are not allowed in an email address include:

  • Exclamation mark (!)
  • Number sign (#)
  • Dollar sign ($)
  • Percent sign (%)
  • Ampersand (&)
  • Tilde (~)

Lower-case characters, numbers, dashes, and the underscore are allowed in your email address, though some email providers do distinguish between case in the spelling of a valid address.