Parent task for all the improvements to account registration, especially to limit number of spam accounts:

• enforcing providing valid e-mail (present subtask)

• limit number of registrations from given IP in the time-window;

• utilize proxy RBL to detect possible abuse and block registrations from it;

• utilize CAPTCHA:

  • XEP-0158: CAPTCHA Forms ? (https://blog.process-one.net/preventing_spammers_from-abusing_in-band_registration_in_ejabberd/)

  • EJAB-1262: Support CAPTCHA in In-Band Registration

  • Conversations: Implemented account registration with captcha

  • XEP-0389: Extensible In-Band Registration