Service for sending SMTP emails for a forum?

Question

Email

In general, I report I set up and configured the forum, created mail in Yandex PDD, attached a domain, set everything up, added all the necessary DNS in Cloudflare, rolled up to the ssmtp server. Everything worked great. Recently I decided to move to Hetzner. I also set everything up, but when registering on my forum, messages do not come to registrants, they come only if you click "Resend mail" after registration, but not right away.
Server log:

Jun 10 13:23:07 falk sSMTP[911]: SSL connection using ECDHE_RSA_AES_256_GCM_SHA384
Jun 10 13:23:08 nuremberg sSMTP[911]: 554 5.7.1 [2] Message rejected under suspicion of SPAM; https://ya.cc/1IrBc 15rf484588-kPrfroCCnS-N7XFr4bG I

wrote to Yandex support and they say:
Any site for sending letters uses a special server - SMTP. It does not always belong to the company where the mail is located.
Sending emails from your site is now configured via the Yandex SMTP server. Our server is not designed to send automated emails and newsletters, so restrictions apply.

I believe they have restrictions on Hetzner's IPs.
What's the way out of this? I don’t want to register my mail, because it’s easy to burn the IP address of the server behind Flara using it and it will be easier to zaddosit. Therefore, I decided to set up Yandex mail. Is there any adequate alternative? I signed up for Mailchimp, but did not understand how to use this service as a non-mass mailing to specific addresses...

Answer 1

https://aws.amazon.com/ru/ses/

Answer 2

I would advise a variant of some third-party SMTP
https://7fk.ru/nastroyka-smtp/ here I sketched on this issue, lately everyone has been blocked very often