How do people solve the problem of unlimited sending emails during registration?

Question

Fight against spam

I want to write a simple email registration. The scenario is the most common: the user enters some data, his password and email address. Then I send the user an email with a special link, by clicking on which he confirms the mail.
Question:
It turns out that some bad guy can write a program that will constantly register new users on random mailboxes. How to deal with this problem? Add captcha after nth number of repetitions? Or maybe a delay between sending emails?

Answer 1

queue
+ security system - checking
the uniqueness and deliverability of all more or less serious services, just in the background of
captcha, by the way, is not very useful - only a trump card thrown to the attacker

Answer 2

The problem is described in detail here .
Do doulbe opt-in, i.e. validate the e-mail address, do not insert UGC into emails before validation, so that there is no temptation to use you to send spam.