Domain mail on another server problem

[monster-it]

Good Morning,

We have a domain name which is used on another mail server and not office 365 let's say consto.uk this is in our active directory and and we have azure ad sync turned on our domain to office 365 which is actually consto.co.uk but now all of a sudden any mail to helpdesk@consto.uk is getting a wasn't found at error for office 365 how i can let MS office know that mail is not sent through to office 365 but actually its a remote smtp server?

[#2]

If that domain shouldn’t be on Office 365 and you have Azure AD Connect In AD move all the addresses on that domain out of the synchronising OU and then remove the custom domain from Office 365

Alternatively if all those addresses are in a specific OU use filtering in Azure AD Connect to ensure that OU doesn’t synchronise to 365, and again, remove the domain from Office 365.

Hope that helps,

Best, Chris

[#3]

And if you want the domain in office 365 you could, but check the DNS records for that domain! This is were you set were the mailserver is (MX) etc..

[#4]

If you want to continuea using the OnPrem server for e-mail, simply disable Exchange Online for your users and you should be fine