How to register a user and not get into spam?

Question

Mail server

Suppose the situation is: there is SPF, DKIM, the DMARC policy is configured, mail-tester praises the test letter with a score of 10/10.

And now you proudly go to cut the registration system, did everything in beauty: front-end regexes that check the entered value even before attempting to send, the most cruel captchas, sending confirmation to the user - and only then sending out mailing lists.

But all of a sudden, the host of your shared server blocked the ability to send letters, because someone was very diligently entering their non-existent address in the registration form. But what if there are hundreds of such people?
upd: why is everyone so attached to this shared'u?) the example is clearly exaggerated

You can’t even blame the hoster, because if you do this on your server, then sooner or later you will be rejected by a third-party mailer due to the large number of unsuccessful sends. But there may be other, more attentive users on it.

And so I just wondered: how do normal people deal with this? I myself have never encountered this, I cannot programmatically check the existence of the box, and the services for this are far from accurate. Nevertheless, it is difficult to even imagine the presence of such problems on large sites.

Answer 1

But what if there are hundreds of such people?

If you have a super-popular resource (since the percentage of pests is strictly less than 1% always), then what the hell

shared server

?
And the method of struggle is generally standard, but unfortunately in the consequences and not a warning one:
1. Three or four MX records (with priority 10, 20, 30, 40) and 3-4 different IPs to them
2.

sooner or later you will be rejected by a third-party mailer

- got into the black list - temporarily disable its MX and start a long, tedious procedure of "reputation cleaning" either by yourself (letters of compassion addressed to the banned mailer) or with the help of the hoster to which the IP belongs. When this IP comes out of spam, you turn it on again in MX and so on in a circle the eternal struggle of a beaver with a donkey :)

Answer 2

Of course, before sending a verification letter to the sender, the form checks the regexp validity, the MX record, and the existence of such an E-Mail account (via an SMTP session).
The existence of all E-Mail addresses to which the mailing will be made - yes, this is a problem. But they can also be checked (in an SMTP session), at the cost of the speed of the sending itself, of course.
Well, of course, you immediately need to book more IP addresses for the SMTP server, because they will be fought against (nobody personally gave you consent to receive mailing lists, right?).

Answer 3

A week ago, I explained to Timeweb that their robot blocked our mail according to this scenario. Immediately unblocked, we live on. This situation happened for the second time, in my opinion, in the ten years of the existence of a site with 100k users. Nothing critical...