Mails have a state 'received' and I wonder the exact usage of this state.

Does an outgoing mail turns to 'received' when the mail is received by the recipient or is this a state for incoming mails?

I am using only outgoing mails and they stay in 'sent' state (I guess the SMTP server should return something to inform if delivered properly to be able to change the state to received).

I am using MS Office 365

Anyone can help?

Thanks