What an MX record does
Every domain that receives email has at least one MX record, a DNS entry that tells the internet where to deliver mail for that domain. When someone sends an email to you@yourdomain.com, their mail server looks up your MX record to find the correct destination. Change the MX record, and you change where all incoming mail goes first.
How an email gateway fits in
An email gateway sits between the internet and your existing mail provider. You point your MX record at the gateway's hostname. The gateway receives all incoming mail, filters it, and forwards clean mail on to your actual provider: Office 365, Google Workspace, or anything else. Your provider never changes. Your users notice nothing except a cleaner inbox.
The one DNS change
In your DNS provider's dashboard, find the MX record for your domain and update the value to point at the gateway hostname. The priority value (typically 10) stays the same. Before making the change, lower the TTL to 300 seconds. This makes the change propagate quickly and means you can roll back in minutes if needed.
What happens during propagation
DNS changes take time to propagate, typically 5 to 30 minutes with a low TTL. During this window, some mail will route to the old destination and some to the new one. This is normal. No mail is lost; it's all being delivered, just to different endpoints temporarily.
Verifying it worked
Once propagation is complete, use any MX lookup tool to confirm your domain's record points at the gateway hostname. Then send yourself a test email from an external address and confirm it arrives. If it does, the gateway is live and filtering is active.