Emails are not coming to gmail, what could be the problem?

Question

linux

Emails are sent normally mail()using swiftmailer .
Mail.ru mail reaches instantly, and everything is empty on gmail, both in the inbox and in the spam folder.
Until recently it worked, now it doesn't. OS - Ubuntu 16.04
What could be the reason why emails are not coming to gmail?

Answer 1

On the server, the settings were not made, I don’t know exactly which ones, the TP solved such a problem for me.
Contact your host for help.

Answer 2

Check emails in spam filters, in my experience I sin against hosting admins.