I want to create a completely anonymous account on a hosting service, like rapidgator or 4shared and the like, but you need to supply an email account, which apparently cannot be created using Tor or Tails.
Where could I find some guidelines?
It is quite possible to create a quazi-anonymous account without Tor, but to do it, you need to understand how monitors make connections between accounts.
Most of the time, a person attempting to connect two disconnected identities will look for either a common username, a common email, a common password, or a common ip address. Tor takes care of the common ip address, but the other things must be done yourself.
Make sure to both a unique username and password. It is not often that they will check for a password, but in the case that you use the same one twice, it could result in your accounts being "cracked" (the proccess of randomly trying passwords on accounts, until you get a working combonation).
A temporary email address is not hard to get. There are many websites, for instance temp-mail.org provides many easily accessable email addresses that can be used for temorary accounts. If you plan on having an account for an extended period of time, use an email service that does not require much information about yourself, such as cockmail or gmx.
I hope this helps.
Nothing is completely anonymous, but you may register an email account in Riseup using Tor. Do provide a fictitious credentials when you register for the email. This may not be completely anonymous, but it is relatively anonymous. Use the email account only for one purpose and nothing else. For anything else create a new email account. Thus the email account should be single purpose meaning only use it for a single website. This is to eliminate possibility of correlation analysis among different web sites you may visit and using that to make a profile out of your behavior. One other security precaution you may observe is to limit the time period you use an email account. For example you only use an email account for period of one week or 20 minutes or whatever period of time you decide is right for you, and never use that account anymore, even cancel and delete the account after one week or 20 minutes and so on, if possible. Temp-mail usually do this part automatically for you after one time use or period of about 10 minutes.
Like Roya said, achieving perfect anonymity is quite hard if not impossible. However there are some things that you can do.
These are some basic steps which help to protect your anonymity. However when thinking about it you might encounter more things to take care of. Remember to work proactively. It is not possible to protect your anonymity, when your identity is revealed.