You’ll set up Office 365 to use your custom domain, add the Office 365 accounts, and then forward email for the users with Office 365 accounts.

Before you get started, read this article to learn the additional setup steps and understand the limitations of this approach:

• Your current email provider must provide email forwarding.
• You need to manage your Office 365-related DNS records at your DNS hosting provider, rather than having Office 365 manage these records for you. To learn what this entails, see Add your domain to Office 365 without redirecting your name server records.
• Some Office 365 features won’t be available:
  • Office 365 users won’t be able to see free/busy information for the users who are on the other email provider.
  • Admins won’t be able to administer everyone’s accounts from one place.
  • Office 365 users may not be able to use Office 365 spam filtering (see step 3).

If you’re using Office 365 Enterprise or Office 365 Midsize Business:

Don’t follow the steps in this article.

• Instead, follow the steps to set up a pilot in FastTrack.
• Or if you have an on-premises Exchange server, see Hybrid configuration.

Example

Margie’s Travel has 5 employees. Margie and her husband, Mike, want to use the advanced features offered by Office 365 so they can keep an eye on the business from their mobile devices. All 5 employees have their email hosted by A. Datum Corporation, who hosts their website and provides basic IMAP-based email. All contacts, tasks, and calendaring is done locally on Outlook, as they have no Exchange server. Although Margie expects to move her other 3 employees to Office 365 at some point, for the moment, she wants to begin using it with her husband before they decide to move everyone to the cloud. She wants no impact to her customers, so she doesn’t want to change any email addresses.

Margie notes the limitations described above, and decides that they won’t be a problem for her. Because there are only 5 employee mailboxes, Margie won’t have to do too much ongoing administration. Sue, Sally, and Scott don’t use their calendars much today (other than for keeping their own personal schedules), and their mailboxes are hosted on an IMAP server that doesn’t support these features, so this simple solution is perfect for their needs.

Starting configuration:

Desired configuration:

Changes are shown highlighted in blue.

Step-by-step guide

Step 1: Verify that you own the domain you want to use

1. Sign to Office 365.
2. Go to Admin > Manage your email and website domains.
3. Click Add a domain.
4. Type the domain, for example margiestravel.com, and then click Next.
5. In the drop-down list, select your DNS hosting provider, and follow the instructions to add a TXT record to show that you own the domain. If the instructions for verifying the domain show using an MX record, be careful when entering the Priority information. This MX record is only used for verifying that you own the domain, and is not used for mail routing. It must be lower priority than the existing MX record that routes email through A. Datum.
6. Click done, verify now. It takes between a few minutes and 72 hours for DNS changes to take effect.
7. When verification is successful, you’ll be asked to modify your DNS name server records.
   Don’t modify the name server records. Instead, click Cancel to exit the wizard.

Step 2: Mark the domain as shared in Exchange Online

1. Follow the instructions for accessing the Exchange admin center (EAC).
2. In EAC, click Mail flow.
3. Under Accepted Domains, double-click the domain you want to modify, for example, margiestravel.com.
4. In the pop-up window, select Internal relay domain.
5. Click Save. This setting may require a few minutes to take effect.

Step 3. Whitelist the existing email server

This step is optional.

Office 365 uses Exchange Online Protection (EOP) for spam protection. If EOP detects a high volume of spam being forwarded by the A. Datum mail server, it may block the A. Datum server, which would prevent forwarding from working. If you are confident with the spam protection your other email provider uses, you can whitelist their server in Office 365. However, this will also allow any spam that arrives through A. Datum to come through to the Office 365 mailboxes, and you won’t be able to evaluate how well Office 365 prevents spam.

1. Follow the instructions for accessing the Exchange Admin Center (EAC).
2. In EAC, click Protection, and then click Connection filter.
3. In the IP Allow list, click +, and add the IP address for the mail server. You can get this from your current email provider.

Step 4: Create user accounts and set the primary (reply-to) address

1. Sign in to Office 365. (If you’re in EAC, click Admin to go back to Office 365.)
2. Click Add users, reset passwords, and more.
3. Create the user accounts. In this example, we’re creating accounts for Margie and Mike.
   1. Click +, and fill out the required information.
   2. To keep Margie and Mike’s email the same as it is currently, the User name field should be exactly the same as the user’s existing email address.
   3. In the second box under User name, select your custom domain name.
4. Click Save.

Note If you open the properties for Margie and Mike in EAC, notice that the @margiestravel.onmicrosoft.com address remains as an additional SMTP address.

Step 5: Update DNS records at your DNS hosting provider

Sign in to your DNS hosting provider’s website, and follow the step-by-step insructions to create all required Office 365 DNS records, with the following important exceptions:

1. Do not create a new MX record or change your existing MX record.
2. If you already have a Sender Policy Framework (SPF) record for your previous email provider, instead of creating a new SPF (TXT) record for Exchange Online, just add “include:outlook.com” to the current TXT record. For example, “v=spf1 mx include:adatum.com include:spf.protection.outlook.com ~all”.If you don’t have an SPF record yet, modify the one recommended by Office 365 to include the domain for your current email provider, plus protection.outlook.com. This authorizes outgoing messages from both email systems.

Step 6: Set up email forwarding at your current provider

At your current email provider, set up forwarding for Margie and Mike’s email accounts to your onmicrosoft.com domain:

• Margie’s A. Datum mailbox should forward to margie@margiestravel.onmicrosoft.com
• Mike’s A. Datum mailbox should forward to mike@margiestravel.onmicrosoft.com

When you complete this step:

• All mail sent to margie@margiestravel.com and mike@margiestravel.com will be available in Office 365.
• When Margie and Mike reply to mail they receive, the Reply-to address will be margie@margiestravel.com and mike@margiestravel.com.

Notes

• Contact your current email provider for the exact steps for setting up forwarding.
• You don’t need to keep a copy of messages at the current email provider.
• Most providers forward email leaving the Reply-to address of the sender intact, so that replies go to the original sender.

Step 7: Test mail flow

1. Sign in to Outlook Web App (OWA) using Margie’s credentials. The URL is https://outlook.com/owa/office365.com.
2. Perform the following tests:
   1. Test local Office 365 email. For example, send an email to Mike (mike@margiestravel.com). This email should be delivered immediately. In this scenario, the message will not be routed to Mike’s mailbox on A. Datum because Office 365 sees the mailbox as being local.
   2. Test email to someone who’s on the other email system. For example, send an email to Sue. This email should be delivered to Sue’s mailbox on the A. Datum server.
   3. From an outside account, or from an employee’e email account on the other email system, verify that forwarding is set up properly on the other email system. For example, from Sue’s A. Datum account or a Hotmail account, send Margie an email and verify that it arrives in Margie’s Office 365 mailbox.

Step 8: Move mailbox contents

Since there are only two users to move, and since Margie and Mike are both using Outlook today, the email can be moved by opening the old .PST file in the new Outlook profile and copying the messages, calendar items, contacts, etc. Once organized in the proper locations in the Office 365 mailbox, the items can all be accessed from any device, anywhere.

When more mailboxes are involved, of if the employees are not already using Outlook, you can use the migration tools available in the Exchange admin center. To get started, go to the Exchange admin center, and follow the directions in Migrate Email from an IMAP Server to Exchange Online.