Are email addresses case sensitive

Question

I ve read that by standard first part of e-mail is case sensitive  however I ve tried to send e-mail to name example com  Name example com and NAME example com - it has arrived in each case   How do mail servers handles usernames  Is it possible to miss with case and that message wouldn t be delivered  Is it really very important to use exactly same letter case  as was written while registering when giving your e-mail address

User · Answer

IETF Open Standards RFC 5321 2 4  General Syntax Principles and Transaction Model      SMTP implementations MUST take care to preserve the case of mailbox   local-parts  In particular  for some hosts  the user  smith  is   different from the user  Smith        Mailbox domains follow normal DNS rules and are hence not case   sensitive

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Way late to this post  but I ve got something slightly different to say      gt  gt   Are email addresses case sensitive     Well   It Depends      TM    Some organizations actually think that s a good idea and their email servers enforce case sensitivity   So  for those crazy places   Yes  Emails are case sensitive       Note  Just because a specification says you can do something does not mean it is a good idea to do so    The principle of KISS suggests that our systems use case insensitive emails   Whereas the Robustness principle suggests that we accept case sensitive emails   Solution    Store emails with case sensitivity Send emails with case sensitivity Perform internal searches with case insensitivity   This would mean that if this email already exists   user x com      and another user comes along and wants to use this email  USER x com      that our case insensitive searching logic would return a  That email already exists  error message   Now  you have a decision to make   Is that solution adequate in your case   If not  you could charge a convenience fee to those clients that demand support for their case sensitive emails and implement custom logic that allows the USER x com into your system  even if user x com already exists   In which case your email search validation logic might look like something this pseudocode   if  user paidEmailFee          case sensitive email    query    select   from users where email LIKE     user email        else         case insensitive email    query    select   from users where email ILIKE     user email          This way  you are mostly enforcing case insensitivity but allowing customers to pay for this support if they are using email systems that support such nonsense   p s  ILIKE is a PostgreSQL keyword   http   www postgresql org docs 9 2 static functions-matching html

User · Answer

Per  l3x  it depends  There are clearly two sets of general situations where the correct answer can be different  along with a third which is not as general  a  You are a user sending private mails  Very few modern email systems implement case sensitivity  so you are probably fine to ignore case and choose whatever case you feel like using  There is no guarantee that all your mails will be delivered - but so few mails would be negatively affected that you should not worry about it  b  You are developing mail software  See RFC5321 2 4 excerpt at the bottom  When you are developing mail software  you want to be RFC-compliant  You can make your own users  email addresses case insensitive if you want to  and you probably should   But in order to be RFC compliant  you MUST treat outside addresses as case sensitive  c  Managing business-owned lists of email addresses as an employee  It is possible that the same email recipient is added to a list more than once - but using different case  In this situation though the addresses are technically different  it might result in a recipient receiving duplicate emails  How you treat this situation is similar to situation a  in that you are probably fine to treat them as duplicates and to remove a duplicate entry  It is better to treat these as special cases however  by sending a  quot reminder quot  mail to both addresses to ask them if the case of the email address is accurate  From a legal standpoint  if you remove a duplicate without acknowledgement permission from both addresses  you can be held responsible for leaking private information authentication to an unauthorised address simply because two actually-separate recipients have the same address with different cases  Excerpt from RFC5321 2 4   The local-part of a mailbox MUST BE treated as case sensitive  Therefore  SMTP implementations MUST take care to preserve the case of mailbox local-parts   In particular  for some hosts  the user  quot smith quot  is different from the user  quot Smith quot    However  exploiting the case sensitivity of mailbox local-parts impedes interoperability and is discouraged

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I know this is an old question but I just want to comment here  To any extent email addresses ARE case sensitive  most users would be  very unwise  to actively use an email address that requires capitals   They would soon stop using the address because they d be missing a lot of their mail    Unless they have a specific reason to make things difficult  and they expect mail only from specific senders they know    That s because imperfect humans as well as imperfect software exist   Surprise   which will assume all email is lowercase  and for this reason these humans and software will send messages using a  lower cased version  of the address regardless of how it was provided to them   If the recipient is unable to receive such messages  it won t be long before they notice they re missing a lot  and switch to a lowercase-only email address  or get their server set up to be case-insensitive

User · Answer

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

[email] Are email addresses case sensitive?

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