in the past few days, our registration page wasn’t working. This was due to two separated issues, both solved today:
1) Our .aspx host Databasemart did move our website, so we had to update a couple links.
2) While investigating this, we realized that Mandrillapp (that we were using to send registration emails) stopped work, so after reading this fine article (http://www.codeinwp.com/blog/mandrill-alternatives/) we moved to Sendinblue.
Everything should be working fine now.