TXT Record

A TXT record is a DNS entry that just stores a string of text. It was originally for notes. Now it's the workhorse of domain verification and email authentication.

When Google, Microsoft or a marketplace asks you to "add a TXT record to verify ownership," they're asking you to publish a code only the domain's DNS controller could publish. SPF, DKIM and DMARC, the three rules that decide whether email from your domain lands in the inbox or in spam, are all TXT records too.

If you buy a domain and plan to send email from it, expect to set all three. If you sell a domain, expect the buyer to ask you to add a verification record if the transfer is going to take a while.