How to set up mail.php so that mail is not banned?

Question

Mail for domain

Good afternoon. Client sites have a form for submitting, for example, ask a question, testimonials, etc.
We don’t have our own mail server, in the mail.php file we use a mailbox on Yandex. The problem is that after some time Yandex blocks it and you need to change the password on the mailbox and, accordingly, in the mail.php file for each client.
How can this issue be resolved? Registering mail for every 5-10 clients is not very convenient.
They suggested this option, start mail for the domain on Yandex and be sure to register dkim there. I registered the domain, delegated DNS to Yandex, created mail, dkim was already registered automatically. So mail is sent and received from the mailbox. But I'm still afraid to change it on clients. Suddenly it won't work.
Maybe someone already faced a similar problem and found a solution? Unfortunately, I do not have enough knowledge in this matter. I would be glad for any hints. Thank you.

Answer 1

It is not necessary to send letters through PDD or any other mailbox service, they are not intended for this. Letters must be sent directly or through special mailing services. To send directly you need to:
1. Publish a separate DKIM selector, configure the signature for this selector directly on the server, make sure everything works.
2. add the server's IP address to the SPF of the domain
3. Make sure that the correct address is used both in the From: field and in the SMTP envelope (envelope-from), in the incoming letter it is usually shown in the Return-Path header.