How to save all sent mail of users?

Question

SMTP

Hi people.
The management set the task to save all sent mail of certain employees. Mail is hosted on yandex.ru. There are mail programs on computers (that is, people do not go directly to the yandex.ru website). Tell me the easiest way to do this, so that in the end you can see in a digestible form which employee sent what and where.
Thank you all in advance.

Answer 1

You declare to the management that you are not a magician, say that you need investments in your own mail server.
You buy a VPS, put your postfix + roundcube mail, for example, another web muzzle, and there you already twist it as it should, save, backup.
Do not allow external mail in the office.

Answer 2

What program? Is the connection encrypted? with the mail server.
Mail personal or work?only

Answer 3

Provided that all employees use Yandex via IMAP and the sent letters are on the server, create an account in which you can set up mail from the accounts of those employees who need to be monitored.
If the mail program uses POP3, then this is not feasible.