You don't enter an email address. You click the option given to you for those without email addresses, in which case you will be asked to upload proof of employment, which could be a pay stub from the last 90 days, your current employee ID (really nice if it has an expiration date on it, like gateway IDs do), or a couple other things. I just re-verified my eligibility last week with Sprint.
I stay with Sprint because:
1.We have a long history now, that dates back to 2004. Thus, recently I had a family member asked to join my account. I had ten lines, the max for a regular consumer account. Sprint went ahead and approved me for an eleventh, although technically once someone goes past ten lines they are supposed to be upgraded to a business account, requiring a business ID.
2.No one else has a sufficient amount of wireless data; Sprint's is still unlimited, and they have upgraded their infrastructure, although it still can be insufferable at times. I have used 60GBs in one month on my phone (and I do have a wifi system at my house), so I am not impressed with plans that offer 12 or even 20 gigs.