How to set up mail on a web server?

Question

Email

Hello. There are several vds servers on ubuntu, mail goes to them via sendmail. There were no particular problems, when suddenly the servers began to fall into the spam database, then just into spam. On it decided to recustomize sending of mail. There were two options:
1. Connect dkim to sent messages. Mail for the domain is from Yandex and DNS settings are stored there. But normally I did not find instructions that would work for me.
2. Send all mail from the server via smtp, but again, I didn’t find the instructions, and it’s not realistic to prescribe this for each site in php, because many sites.
Prompt with good advice (except to hire a direct admin) and a good link.
Thank you.

Answer 1

Not on the web server.
You can set it up, but the web server will be out of business here.
1. Write the spf in which you specify, among other things, the IP address of your VPS
2. Install postfix and configure DKIM, searching for postfix dkim will give you three dozen ready-made instructions.
3. Hire an admin.