If Microsoft 365 is handling your business email, DNS has to tell the internet two things: where incoming mail should go, and which systems are allowed to send mail for your domain.
Most problems come from mixing old hosting mail with Microsoft 365. The website can stay on your web server, but email routing, authentication, and client setup must point to Exchange Online.
Core idea
MX records decide where incoming mail is delivered.
For Microsoft 365, the MX record should point to the mail protection host shown in your Microsoft admin centre, for example example-com.mail.protection.outlook.com.
Remove old MX records that point to a Plesk, cPanel, or hosting mailbox server unless you are deliberately running a hybrid setup.
Authentication
SPF, DKIM, and DMARC decide whether other servers trust the mail you send.
For a Microsoft-only setup, SPF should normally be v=spf1 include:spf.protection.outlook.com -all. Use one SPF record only; multiple SPF TXT records can cause failures.
DKIM should be enabled in Microsoft 365 with the two selector CNAME records Microsoft provides. DMARC can then sit on top of SPF and DKIM to tell receivers what to do when authentication fails.
Client setup
Autodiscover helps Outlook find the right mailbox settings.
Add a CNAME for autodiscover pointing to autodiscover.outlook.com. Without it, users may still be able to sign in, but Outlook setup and profile repair become less reliable.
If old mail clients still send through mail.yourdomain.com, they will fail SPF once your SPF authorizes only Microsoft 365.
Plesk trap
Disable local mail service when the domain moves to Microsoft 365.
On Plesk, local mail can keep trying to deliver mail for your domain inside the server even after public MX records point to Microsoft 365.
If the same server receives mail for other domains, also check its DNS resolver cache. A stale resolver can reject valid Microsoft 365 messages because it still sees an old SPF record.
Checklist
The minimum clean Microsoft 365 DNS set.
Use one Microsoft MX record, one Microsoft SPF TXT record, one autodiscover CNAME, two Microsoft DKIM CNAMEs, and one DMARC TXT record.
Keep the website A record unchanged if the website is still hosted elsewhere. Moving email to Microsoft 365 does not require moving the website.
Quick DNS checklist
- MX points to Microsoft 365 mail protection
- SPF includes spf.protection.outlook.com
- Only one SPF TXT record exists
- Autodiscover points to autodiscover.outlook.com
- DKIM selector records are added and enabled
- Plesk local mail is disabled for the domain
Want me to check your Microsoft 365 mail setup?
I can review the DNS records, Plesk mail settings, Outlook setup, and SPF/DKIM/DMARC alignment before you lose more time to failed delivery.