How to setup or add new custom domain in M365 Portal

The problem: your custom domain shows as “added” in Microsoft 365, but email is broken.

Adding a custom domain looks simple. You enter the domain, verify it, see a green tick, and move on.

Then the issues start:

⚠️ Email never arrives, because the MX record still points to the old provider

⚠️ Outlook and Teams sign-in fail or behave oddly, because the Autodiscover and service CNAME records are missing

⚠️ Users can’t sign in or end up with the wrong address, because the domain was made the default before anything was tested

⚠️ Old email addresses stop working, because nobody set up aliases

Most quick tutorials stop at verification. That’s the step that looks done, not the step that makes email work.

Why it matters:

One missed DNS record can stop email for everyone on the domain. Usually nobody notices until a customer says, “I emailed you three days ago.”

✅ The fix: follow the whole process, not just the part that looks done

🔹 Email never arrives → add the correct MX record so mail is routed to Exchange Online

🔹 Outlook and Teams problems → add the TXT, CNAME and Autodiscover records for Exchange and Intune, and understand what each one does

🔹 Sign-in problems → test mail flow and sign-in before making the new domain the default

🔹 Lost addresses → assign the domain to users carefully and keep old addresses as aliases

In my latest XantheTech video, I walk through:

✅ Adding and verifying the domain (including Cloudflare Domain Connect)

✅ The exact DNS records you need and why each one matters

✅ Adding records manually, with TTL explained

✅ Setting the default domain safely

✅ Assigning the domain to users and testing sign-in

✅ The user impact and how to manage email aliases

🎥 Watch here: https://youtu.be/0jGTlPjPTKY

Have you seen email break after a domain setup? What was the missing piece? 👇

#Microsoft365 #ExchangeOnline #DNS #EntraID #M365Admin #ITAdmin #EmailSetup #XantheTech