Are Emails Case Sensitive? Piecing Emails Together Letter by Letter 

are emails case sensitive cover image with an old typewriter

Does it matter if you use uppercase letters in an email address? Will the email reach its destination? 

Here’s a straightforward answer to ease your mind: technically, email addresses can be case-sensitive. However, in practice, most email systems are pretty forgiving. So, whether you accidentally capitalize a letter or not, it’s unlikely to stop your email from being delivered correctly.

Curious to learn more? Join us as we explore the best practices for choosing and using email addresses. 

Email Addresses Have Two Parts 

A valid email address has two parts, each following specific rules to ensure that email servers can read the address properly.

The two parts are: 

  • Username: This is the part before the @ symbol, also known as the local part of the email. It’s your unique identifier. You can use up to 64 alphanumeric characters — Latin letters and the numbers 0 through 9.
  • Domain: The part after the @ symbol is your email domain. It tells the system where to send your email. You can include up to 255 Latin characters and numbers from 0 to 9. It’s usually the same as your website domain, like

Next comes the fun part! 

Are Emails Case-Sensitive? A Technical Answer 

Email communication uses several standard protocols to work properly. To understand if emails are case-sensitive, we need to look at two key protocols. 

They are:  

The details of each protocol are outlined in documents called Requests for Comments (RFC). According to RFC5321 (SMTP), the local part of an email address (the part before the @ symbol) can be case-sensitive. 

However, RFC3501 (IMAP4rev1) says that devices must handle both case-sensitive and case-insensitive email addresses. A more recent update in 2021 (RFC9051) has moved towards only recognizing case-insensitive addresses.

Because of these standards, pretty much all email services, including Gmail and Yahoo, ignore whether you use uppercase or lowercase letters in your emails.

Use Capitalization to Your Advantage 

So far, we’ve established that capital letters in email addresses are harmless. But they can be helpful. 

For one, capitalization improves readability and recognition. When clients and partners see an email address that’s easy to read, like, they’re more likely to remember and type it correctly. 

Capital letters also emphasize important elements in an email address. If your company name is two words, like Silver Leaf, an address like immediately makes your company name stand out. This small tweak can make communications smoother and reduce the chances of emails going astray.

Finally, email addresses can be powerful tools in marketing. Consider incorporating a call to action directly in the email address. For example, use for a campaign to motivate customers to take action. This method turns a simple point of contact into an active part of your marketing strategy.

Exploring Case Sensitivity Beyond Email Addresses

You can use capitalization to your advantage throughout your emails to enhance your message clarity and readability. Let’s see how. 

Subject Line 

An email’s subject line isn’t case-sensitive in terms of deliverability — whether you type in uppercase, lowercase, or a mix of both, your email will reach its destination just the same. However, the way you use capitalization affects how your message comes across. 

Writing in all caps might come across as shouting, and it may cause your email to end up in the spam folder. On the other hand, lowercase can seem casual. 

Use capitalization strategically to draw attention to the critical words in your subject line and improve your open rates. You can capitalize the first letter of each major word or write the most important in all caps. 

For example, in an abandoned cart subject line, you can capitalize the word “DISCOUNT” or “DEAL” to attract attention. 

Body Text 

Your email content and email sign-off follow similar rules in terms of deliverability. Still, proper capitalization helps with readability and professionalism. Use standard capitalization for proper nouns, the beginning of sentences, and other grammatical norms. This keeps your message clear and easy to follow.

However, in some cases, email copywriting tricks can bend capitalization rules for creative or persuasive effect.

Building on our abandoned cart email, you can use title case phrases like “Don’t Miss Out!” or “Last Chance to Save!” to draw attention to your email call-to-action


Just like the body text, email footers benefit from consistent capitalization. Pay attention to details like your company name, contact information, and legal disclaimers. Proper capitalization here adds to the professional appearance of your emails.

The Inbox Formula: Your Guide to Dodging Spam Filters 

If you’ve ever worried about your emails ending up in the spam folder, the “Inbox Formula” guide is exactly what you need. 

Our comprehensive guide explores the crucial aspects of email deliverability, including how to format your email addresses and subject lines to avoid being flagged as spam. 

You’ll also learn: 

  • How to establish credibility with ISPs. 
  • Why you need email authentication protocols. 
  • How to sustainably scale your email sending capacity, and more. 

Grab your copy of the “Inbox Formula” today and say goodbye to the spam folder! 

Are Special Characters Allowed in an Email Address? 

Different platforms can set their own rules about which characters you can use in a username. 

In general, we recommend only using letters and digits in your email address because you never know which characters a sending or receiving server prohibits. 

These are Gmail’s requirements, which are pretty standard across the industry: 

  • You can use letters (a-z), digits (0-9), and dots (.).
  • You can’t use these characters:
    • Spaces, 
    • Ampersand (&),
    • Equals sign (=),
    • Underscore (_), 
    • Apostrophe (‘),
    • Dash (-),
    • Plus sign (+),
    • Comma (,), 
    • Brackets (<,>), 
    • More than one dot (.) in a row. 

However, these special characters are less likely to be restricted: 

  • Asterisk (*)
  • Exclamation mark (!)
  • Dollar sign ($)
  • Hash sign (#)
  • Percent sign (%)
  • Tilde (~)

Why are some special characters restricted? 

One reason is that email servers reserve certain characters in the email header for special purposes. 

Another reason has to do with email security because special characters have specific use cases in programming and scripting languages. 

For example, imagine an email service allowing special username characters. A hacker could use a malicious script as their username (for example, an SQL command that deletes all the user data — ‘drop table users’). 

If the website doesn’t properly filter out those characters, the code could be executed. This could lead to sensitive information being stolen or the website being taken over.

SQL injection and Cross-site scripting (XSS) are common examples of attacks carried out using special characters in input fields. Modern email systems have multiple layers of defense against these attacks, but disallowing special characters is a crucial starting point. 

Are International (Non-English) Characters Allowed in Email Addresses? 

Languages like Chinese, Arabic, or Russian often require characters outside of the standard Latin alphabet. There are many reasons why someone might opt for a non-English email address. For example, they may be more comfortable communicating in their native language. 

The original SMTP (defined in RFC5322) didn’t provide a way for international characters in email addresses. 

But in 2012, a new SMTP extension was published to make emailing more versatile by introducing support for non-English characters in email addresses (RFC6531 and RFC6532). 

However, not all servers online may be updated to support this international standard. So, it’s safest to stick with letters and numbers in English to make sure your emails get delivered.

At Campaign Refinery, we’re all for including international symbols in email addresses. Your subscribers can use characters from languages other than English in the local part of their email addresses, and you’ll still be able to send them email campaigns without any issues.

What’s the difference between the new and old standards? 

To understand how international characters became possible in email addresses, you need to know what a character set is. 

In simple terms, a character set defines a mapping between characters (such as letters, digits, punctuation marks, and special symbols) and their corresponding binary representations, which computers understand. Each character is assigned a unique code.

The old system used the ASCII encoding, while the new system uses Unicode characters. 

What are those? 

  • American Standard Code for Information Interchange (ASCII) is a character encoding standard that uses a 7-bit binary code to represent text characters. It mainly includes characters from the English alphabet, digits, and a few special symbols.
  • Unicode is a more comprehensive character encoding system that aims to represent every character from every language in the world, along with symbols and emojis. It supports characters from various writing systems, including Latin, Greek, Cyrillic, Arabic, Chinese, Japanese, and many others.

Best Practices in Choosing an Email Address 

The right email address shows you’re professional, trustworthy, and easy to reach, while the wrong one can leave a negative impression and make communication difficult. Let’s explore some best practices to make sure you make the right choice for both business and personal email addresses.

Business Email Addresses 

With business emails, your core objective is to look professional. Your email address needs to reflect positively on you and your organization. 

Follow these tips when picking an email address for professional use: 

  • Use a combination of your first and last name. If you’re using a company domain, combining your first name with the first letter of your last name gives off a friendly yet professional vibe. Alternatively, using the first letter of your first name with your full last name can give a more corporate feel.
  • Stay consistent across platforms. If you want to use both social media and email as your communication channels, choose the same username for all platforms. This way, you’ll make it easier for your audience to find you everywhere and you’ll increase your brand awareness. 
  • Don’t be repetitive. If your domain is your own name, try not to repeat your name as the local part of your email address. Instead, opt for simple words like “hi,” “hello,” or “me.” These are easy to understand and won’t confuse anyone reading your email.
  • Skip nicknames or abbreviations. It’s best to stick with your full name to come across as more professional. Also, don’t include your job title or credentials in your email address since it might make you seem arrogant or like you’re showing off.
  • Steer clear of using free email providers for business purposes. Custom domain emails tend to look more professional than those from free providers, so it’s worth investing in one for your business needs.

Personal Email Addresses 

For personal email addresses, you have more flexibility to express yourself. However, it’s still important to choose an address that is easy to remember and appropriate for various contexts. 

Consider these guidelines when creating a personal email address:

  • Express your personality. Feel free to incorporate elements of your personality or interests into your personal email address.
  • Keep it appropriate. While personal email addresses allow for creativity, make sure your address is still appropriate for professional communication if needed. An address based on an inside joke or a trending meme might seem funny, but it’ll be embarrassing when you have to give it to a stranger, or someone forwards an email from you
  • Avoid overly complex addresses. While you can be creative, avoid convoluted email addresses that are difficult to remember. We still don’t recommend using special characters, even if you want to be original. 
  • Think about your privacy. Be careful with the information you include in your personal email address to protect your privacy and security. Even a simple detail like year of birth can give attackers a decent starting point to learn more about you and send spoofed emails or conduct phishing attacks

The Campaign Refinery Advantage

At Campaign Refinery, we specialize in ensuring your emails land right where they should: your customers’ inboxes. Because what good is a great email if it never reaches its intended recipient?

We’ve earned a stellar reputation with mailbox providers thanks to our state-of-the-art sending system. 

What makes us unique? 

  • Rigorous approval system for new clients: Every new account must pass through an approval process to block spammers from joining.
  • Mandatory authentication protocols: We require all clients to set up SPF, DKIM, and DMARC before launching their first email campaign. 
  • Powerful tag-based segmentation tools: Organize your email lists just the way you want to boost engagement rates. Both your subscribers and mailbox providers will appreciate it!
  • Automatic list cleaning: Our system cleans out spam traps, complainers, role-based emails, and burner accounts to keep your lists pristine.
  • Engagement gamified: Reward your most engaged subscribers for opening and interacting with your emails. 
  • Robust analytics: Effortlessly spot subscriber behavior trends with our visual analytics dashboard.

Eager to join Campaign Refinery? Apply today and transform every email into an opportunity

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