Why is Google blocking smtp messages from my site?

Question

gmail

In general, my site was sitting on 1 host, sending mail via smtp worked for 1 day, on the second Google blocked my application (via the link from the letter), I allowed access to the application. But the mail did not leave. If through mail, then it goes to spam, if it goes at all. Moved to another host. Same thing with mail. I tried to send via smtp, but received the same error and a letter from Google (as on the previous host). How to be?

Answer 1

what mistake?
how did you move to another host?
what mail system is used?
How is a domain administered?
does it have mx records at all? Is there a write-back? spf? dkim? dmarc?