My language has diacritics, a lot of it. So as in other languages, it is common to omit some (or all) in informal mails, sms, etc. Simply because it takes more effort to type it. Or when expecting that your name would not render on the receiving device.
When searching for a string or typing a name, say “Jérôme” (or “Ondřej” or “Øistein”), in the To field and awaiting the suggestions, only some of the expected pop up. The other Jérômes will not show up as their names are without diacritics (part of the email address, laziness when putting in the address book, …).
To help us out, those speaking and writing difficult languages, lazy and not knowing where to find ß and Ř on a keyboard, the searches should not be sensitive to diacritics.