> That's why we keep your verified mailbox address for sending mail; but there's no good reason to consider them different for the purpose of identity.
Both of Microsoft's own identity services (AAD and Live ID, and by extension O365 and Outlook.com) recognize (and allow creation of) microcolonel@example.com, micro.colonel@example.com, and mic.rocolonel@example.com as distinct identities/email addresses.
What you're saying is that once the first of (microcolonel|micro.colonel|mic.rocolonel)@example.com registers at github, the other two will no longer be able to do so, but will instead receive a confusing 'you already have an account' error, (hopefully) without being able to receive password reset emails.
...and only one in 50,000 e-mail addresses contain the string "rq5", therefore we strip that string from addresses...
A false postive in these identity checks is likely to be less destructive than a false negative. But I still don't get the point of making up all sorts of rules not in the standard. I have seen both + as well as meaningful dots in e-mail adresses in the wild.
+ and . have is legal in email addresses since it was standardized.
Google was the first installation I know of to silently swallow periods. Plus-addressing was well-known back in the day, but as far as I know GUI mailers more or less killed the practice by not offering support for it, and web sites written by people too smart to know how to validate email addresses ensured you can't even use them properly anymore.
That's why we keep your verified mailbox address for sending mail; but there's no good reason to consider them different for the purpose of identity.