At [WayBack] Error when trying to signup using an email address with uppercase letters (#27898) · Issues · GitLab.org / GitLab Community Edition · GitLab, I commented this:
Both the
:email_confirmationfields should get the same case processing treatment.That treatment should consist of this:
- The part before the @ should be treated as case sensitive
- The part after the @ should be treated as case insensitive
This means that:
Foo@Example.OrgandFoo@example.orgare the sameFoo@example.organdfoo@example.orgare differentThe main reason is that there are email systems expecting case sensitivity in the part before the @ sign.
I think excluding those users from being able to use GitLab is a bad idea.
See especially the comments at the Stack Overflow answer to Are email addresses case sensitive?
Relevant RFC 5321: Simple Mail Transfer Protocol sections:
Important comments:
I work at a large company and there is another person with the same first and last name. I discovered today that his local-part differs from mine only in capitalization. This has been working properly, so I was surprised to see “no widely used mail systems distinguish different addresses based on case”. We use MS Exchange which I would call “widely used”. – Matthew James Briggs Nov 24 ’15 at 20:14
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. – Adam111p Apr 27 ’16 at 10:02
Most important parts of the 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”
–jeroen
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