Exceeding Max Email Address Sizes

Read this: http://www.eph.co.uk/resources/email-address-length-faq/ The upshot of it is that you should use 254 characters to store email addresses, because that is the maximum allowed in an SMTP transaction. This is specified in RFC5321 (your article says so, and is actually quoted in mine), which is authoritative.

To be honest, even if someone had a valid email address beyond 256/320 chars it would be a major pain to use.

Anyone using an email address that is even half as big as that (128 chars) needs to trim back!

although on the plus side, they likely get no spam!

For example both of these would be unusable:

//long domain
joe.shmoe@someveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryverylogdomain.com

//long username
someveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryverylonguser@aregularlengthdomain.com