Are email addresses case sensitive?

From RFC 5321, section 2.3.11:

The standard mailbox naming convention is defined to be “local-part@domain”; contemporary usage permits a much broader set of applications than simple “user names”. Consequently, and due to a long history of problems when intermediate hosts have attempted to optimize transport by modifying them, the local-part MUST be interpreted and assigned semantics only by the host specified in the domain part of the address.

So yes, the part before the “@” could be case-sensitive, since it is entirely under the control of the host system. In practice though, no widely used mail systems distinguish different addresses based on case.

The part after the @ sign however is the domain and according to RFC 1035, section 3.1,

“Name servers and resolvers must compare [domains] in a case-insensitive manner”

In short, you are safe to treat email addresses as case-insensitive.

Related Posts:

  1. What is the difference between ports 465 and 587?
  2. Python: What is the correct MIME type for attaching html file to email
  3. How to set SMTP programmatically
  4. How to Configure SMTP on wordpress Cant Send Email
  5. Contact Form 7 + Configure SMTP: Sender email appearing as my own email [closed]
  6. How to setup SMTP for only one specific wp_mail()
  7. Storing Email Account Passwords for SMTP Mailing for a WordPress Plugin
  8. Setting up 2 SMTP accounts: 1 for wordpress and 1 for woocommerce
  9. WordPress ‘on behalf of’ email
  10. Hook into and send mail using WP Mail SMTP type plugin from HTML static front page?
  11. Email Bounce Address
  12. WordPress unable to send mail
  13. SMTP Issues with Office 365
  14. Google Apps SMTP for WP MultiSite?
  15. WordPress SMTP EMail
  16. Is Postfix required for WordPress contact forms in general?
  17. Why is wp-login trying to send an email?
  18. SMTP Error: Could not authenticate [closed]
  19. Getting 400 Error: redirect_uri_mismatch when trying to grant permission to Gmail SMTP plugin
  20. What is the way to hook all wordpress email
  21. how wordpress smtp works? my emailing is not working
  22. Mailing issues with wordpress?
  23. Is it secure to use SMTP password in .php file in WordPress website?
  24. SMTP emails not picking up the correct From name and From email
  25. Send email using wordpress plugin on behalf of someone with their permission
  26. can’t submit mail from contact 7 form site using wp mail smtp
  27. SMTP not working for Comments Email Notifications
  28. SMTP connect() failed
  29. WordPress doesn’t send SMTP email even by phpmailer hook
  30. WordPress stops executing code after the require() method
  31. Sending SMTP mail using a server with self-signed SSL
  32. Email Piping using google apps within WP Engine
  33. Choose from different emails for different purposes
  34. Do SPF Records For Primary Domain apply to subdomains?
  35. Proxy Error 502 : The proxy server received an invalid response from an upstream server
  36. How to send a simple email from a Windows batch file?
  37. Regex empty string or email
  38. SMTP AUTH extension not supported by server
  39. Java regex email
  40. Sending multipart (text/html) emails via wp_mail() will likely get your domain banned
  41. How do you access the Product Short Description in a WooCommerce email template? [closed]
  42. Send Admin Emails to Multiple Email Addresses
  43. How to disable automated E-Mail on PHP error/exception?
  44. Prevent function from triggering again when post in specific category gets another category?
  45. Send batch of posts as HTML Email?
  46. Plugin for Sending Email to Readers about New Posts? (besides “Subscribe2 “)
  47. Disable Admin account being emailed for comment notification
  48. Posting via email, where do I start troubleshooting?
  49. A very basic question – how to properly use wp_mail() in a plugin
  50. WordPress plugin for mail subscriptions [closed]
  51. Email ‘from address’ has a www in it
  52. Add email addresses to already registered users
  53. Is there no way to send email using SMTP without plugin or custom coding?
  54. How to pass external variables to the wp_new_user_notification_email filter?
  55. Send transactional email: first user’s post
  56. Sending email from inside a plugin using PHP PEAR
  57. Send email daily from WordPress site
  58. Can’t send mails using contact plugin [closed]
  59. Is it possible to change an existing post status from ‘pending’ to ‘publish’ via email?
  60. Notify admin on new submit
  61. Howto disable comment moderation emails for admins, but not for authors
  62. Custom Admin Email Subject for Woocommerce (3.8.0) Orders
  63. How to receive an email with WordPress?
  64. How to pass variables to a function argument using add_action [duplicate]
  65. Is it possible to send blog posts via email to subscribers?
  66. How to differentiate between email subscription list and blog subscription list?
  67. Sent comments notifications to multiple users
  68. Need to manually add multiple WP users with same e-mail address (with good reason)
  69. How to stop WordPress from sending mails?
  70. How to add a button to check the emails of my domain?
  71. Send confirmation email when a user’s role is upgraded
  72. Use of antispambot with $curauth->email
  73. Can Postie be used to submit podcasts via email?
  74. Get something out from taxonomy
  75. I want to setup a button/popup/whatever that will prompt users on the site to input their email address
  76. Using wp_mail to send email?
  77. User Without Email?
  78. How do I update user email from frontend input field?
  79. WordPress new user email formatting issues
  80. email saying that was not possible to send the email
  81. could not call wp_email function twice
  82. Paragraph spaces in email template function
  83. Updated : how to make email optional while user registration using default wordpress form
  84. Email post to submitter
  85. Email content as comment
  86. WordPress eMails not working
  87. Contact Form 7 How to Alter the From email address?
  88. Send email to author of the post when the custom post status changes to published
  89. admin-ajax.php returning 0
  90. Check if “Send the new user an email about their account” is ticked
  91. Change wp_mail SMTP settings for each E-Mail
  92. Custom WP deactivate an email activation link sent to user’s email.
  93. How to check “From Email” via WordPress before an email is sent
  94. I used the Buddypress Message Compose to send a site wide email to all members wasnt sent tho [closed]
  95. What is the correct way to send multipart email in wordpress?
  96. Email Subscribe for Downloads in WordPress
  97. Where does email sent to *@example.com go? [closed]
  98. How to send emails and avoid them being classified as spam?
  99. How to change the WordPress email icon?
  100. What’s the optimum way to collect users’ email id?

Leave a Comment