A dismissed employee used corporate mail for his own purposes - how to avoid this?

Question

Information Security

Good day, recently there was an embarrassment at a new job, it turned out that a month ago a fired employee of the IT department used corporate mail and correspondence for his own purposes.
Problems, of course, were on our shoulders, they didn’t bother to change passwords and so on. They wanted to get information about the mailbox from mail.ru, but the administration of the mailbox refused. I would like to know what to do in the future to prevent this?
Thanks in advance!

Answer 1

The problem is purely administrative. Establish a close relationship between the HR and IT departments.
And do not fire an employee without a signature on the bypass sheet, a system administrator.
Accordingly, as soon as the signature is put, the user's data is blocked, passwords and appearances change.
Something like this.
Well, or set all passwords to temporary

Answer 2

turn on the brain and do not start mailboxes on public gmail mail and others,
but give [email protected] mailbox

Answer 3

Well, how do you build security? Do employees know each other's email passwords? If so, then it will be difficult to change anything. In general, the password should be changed every 2-3 months, the change request can be configured automatically.
When an employee is dismissed, we create an electronic bypass sheet, and each admin notes in it that the employee’s access to the services provided has been disabled.
1. Blocked the mailbox - ticked.
2. Blocked the account in AD - ticked.
3. Passed the equipment - ticked.
5. ....

Answer 4

But what if I have mail, why not use it in personal correspondence?
You can restrict sending to allowed domains, otherwise there is no other way.
People in the office worked for me for 15-17 years, they registered corp mail, skype icq, etc. in different social networks, that's when the office was dispersed there were sides for employees to change mail