Should you verify your domain in Office 365 by using a TXT record or an MX record?
Before you use your domain with Office 365, we have to make sure that you own it. Your ability to sign in to your account at your DNS host and create the DNS record proves to Office 365 that you own the domain. Office 365 will look for the record, after you create it, and confirm that you're the domain owner.
The DNS record that you create can be a TXT record or a mail exchange record (MX record). Which one you create depends on your situation:
If your DNS host allows you to create TXT records, we recommend you use a TXT record for verification. TXT records are straightforward to create. In addition, they don’t introduce the possibility of interfering with email delivery if an incorrect value is accidentally entered.
If your DNS hosting provider doesn’t allow users to create their own TXT records, create an MX record for verification. If the steps we provide are carefully followed, your email delivery won’t be affected.
The record that you create doesn’t affect email or any other services. After Office 365 checks for the record and confirms that you own the domain, you can go ahead and delete the record if you like.