That still doesn't make it a good idea to normalize to lowercase. Some people are very particular about capitalization.
MacAdam is a surname, like the Scottish engineer John Loudon McAdam who invented the road construction known as "macadam". "Sandy.MacAdam@example.com" comes across rather different than "sandy.macadam@example.com".
A hypothetical DrAbby@example.com probably would prefer keeping that capitalization over "drabby@example.com".
I'm sure there are real-world examples.
On a related note, I knew someone with an Irish O'Surname who was very particular that the computer systems support his name. (As https://stackoverflow.com/questions/8527180/can-there-be-an-... puts it, "People do have email addresses with apostrophes. I see them not infrequently, and have had to fix bugs submitted by angry Hibernians.") No doubt some of them also want to see the correct capitalization be used.
A possibly better alternative is to recommend that the normalization be used only for internal use, while using the user-specified address for actual email messages, and to at least note some of the well-known issues with normalizing to lower-case.
> A hypothetical DrAbby@example.com probably would prefer keeping that capitalization over "drabby@example.com".
And they can keep that capitalization when they type in their login or otherwise share their email address with the world. Are you suggesting that this Dr. Abby user would be offended that the website’s authentication infrastructure ends up working with it as lowercase?
MacAdam is a surname, like the Scottish engineer John Loudon McAdam who invented the road construction known as "macadam". "Sandy.MacAdam@example.com" comes across rather different than "sandy.macadam@example.com".
A hypothetical DrAbby@example.com probably would prefer keeping that capitalization over "drabby@example.com".
I'm sure there are real-world examples.
On a related note, I knew someone with an Irish O'Surname who was very particular that the computer systems support his name. (As https://stackoverflow.com/questions/8527180/can-there-be-an-... puts it, "People do have email addresses with apostrophes. I see them not infrequently, and have had to fix bugs submitted by angry Hibernians.") No doubt some of them also want to see the correct capitalization be used.
A possibly better alternative is to recommend that the normalization be used only for internal use, while using the user-specified address for actual email messages, and to at least note some of the well-known issues with normalizing to lower-case.