Sometimes involves Web Cookie-s
Some basic things to do during registration/login to reduce rejections, from a friend:
- 60% of our users use GMail where firstname.lastname@example.org is the same as email@example.com (punctuation is ignored on gmail). Your login should behave the same for GMail addresses. This alone brought support case load down by 85%.
- Strip white spaces from login emails and passwords.
- Add mailcheck on signup ( https://github.com/Kicksend/mailcheck ). Lots of people register with every variation of "gnail.com" or "gotmail.com", catch them early.
- treat email addresses as case-insensitive