What are some various email accounts' problems when it comes to creating an account?

“Is it one requires a phone number when not everyone has a phone yet, and another doesn’t ask for (not require) an alternate email address?”
– I mean, not having a phone could be a problem for someone wanting an email account from a site that required a phone number, but most email accounts do not require a phone number at all.
– On the other hand, not asking (nor requiring) an alternate email address does not seem like a problem to me, particularly not for the person creating an account, as it’s the absence of a potential obstacle.

“What are some problems when it comes to creating an email account?”
– THAT list is potentially ENDLESS. I have seen hundreds or perhaps thousands of problems with account-creating systems over the years, including:
* The signup page has poorly-written instructions, so users get confused and don’t do what the page requires to get through the steps.
* The users are confused by some aspect of the signup process.
* The signup process requires some information that the user doesn’t know.
* The signup page requires a field, but doesn’t tell the user the field is required, so it just fails with no explanation.
* The signup page works, but the back-end system takes a while to actually set up the new email account, and the user tries to use it before it is ready, and gets told they can’t, and they give up and never try again.
* The signup system requires the user to have another email, but they don’t have one.
* The signup system requires the user to click on a link on a confirmation email sent to the user’s other email address, but it doesn’t get delivered or goes into a spam folder where the user never finds it.
* The signup system rejects so many user names, that the user gets frustrated and gives up trying to create an account.
* The signup has such complex password requirements, that the user gets frustrated and gives up trying to create an account.
* The signup pages ask questions that the user doesn’t want to answer, so they give up.
* The deal for the email account is a crappy deal in one or more ways (costs money, has terrible limits, has ads, requires you to give them a credit card or ID or something) so users don’t complete the signup process.
* The signup page requires the user to only use certain web browser brands and/or versions.
* The signup page has overly annoying “security questions” that the user must create, which annoys them so much they stop the signup process.
* The signup page requires the user to enter their name and/or birthdate, but it has rules that don’t allow the user’s actual name or birthdate.
* The signup site uses a CAPTCHA that fails for inexplicable reasons (inexplicable other than the usual reason: CAPTCHA SUCKS and/or is itself wrong about its own answers).
* The signup page has bugs where it falsely marks an answer as invalid, even when it is valid.
* The signup page times out, and forgets some or all of what the user had entered so far.
* The signup page has multiple pages, and one of them just fails to load the next page.

And many many more…