Domain mail does not arrive to the recipient

Good day!
I need your help!
have a domain, there are created and mail users when outlook closed letters kicking and do not reach the addressee.
Tell me how to make so that the letter reached the addressee ???
Thanks in advance for your reply!

Has this worked before? I am not sure if the usernames are in the right syntax. To my knowledge the username should not be “user@domain” instead use: “domainusername”.