User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; de; rv:1.9.1.7) Gecko/20091221 Firefox/3.5.7 (.NET CLR 3.5.30729) Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.1.7) Gecko/20100111 Thunderbird/3.0.1 have contact named John.Doe@example.com in my address book. Receive an email from john.doe@example.com the address is NOT matched against the address book, when I edit the contact I can only create a new card. Reproducible: Always Steps to Reproduce: see details Expected Results: email addresses should be handled in a case INsensitive way. wikipedia authors have the following to say about case sensitivity of email addresses (http://en.wikipedia.org/wiki/E-mail_address) "The local-part is case sensitive, so "jsmith@example.com" and "JSmith@example.com" may be delivered to different people. This practice is discouraged by RFC 5321."

From the same RFC you indirectly cited: "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." So doing this would violate that RFC.

See also: Bug 129393