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An error occurred while saving the commentDavid A Bacher commented
Periods are significant in the local part of email addresses per RFC 3522 (https://tools.ietf.org/html/rfc5322#section-3.4.1).
Email addresses are case sensitive, and period, plus and hyphen are significant characters.
It's safe to assume that no sane system administrator is going to set up mailboxes that differ only incase, or where the local name is a bunch of quoted printable Emojis, etc. However, note that I used the word "sane" so there are probably thousands, maybe millions of systems doing it out there somewhere on the Internet. :P
Also, hyphen is valid in the global DNS system, and so whatever you do -- don't just strip it from the whole address. That causes significant problems for users whose domains actually have a minus sign in them.
But if you do this sort of normalization, easiest way is a set of regular expression substitutions based on the domain name. Since the local part is determined by the ISP in question, the rules have to vary and so you worry about the big guys.