hello, I am sending emails with php mail () function from my UPU (Centos 7)
but I have a problem, letters end up in spam, or they don't reach at all (on mail.ru, for example), just postfix, tell me how you can solve this problem? Thank you
Check your server IP address if it is blacklisted (for example via https://mxtoolbox.com ). Mail.ru has a stricter filtering system, so it is possible that letters are simply rejected there because of a suspicious address.
Also, to improve the throughput of letters, configure DKIM, SPF and DMARC correctly. You can see what exactly Mail.ru thinks about your server through their service https://postmaster.mail.ru