Best practices for configuring standalone EOP

Follow these best-practice recommendations for standalone Exchange Online Protection (EOP) in order to set yourself up for success and avoid common configuration errors. This article assumes that you've already completed the setup process. If you haven't completed EOP setup, see Set up your EOP service.

Use a test domain

We recommend that you use a test domain, subdomain, or low volume domain for trying out service features before implementing them on your higher-volume, production domains.

Synchronize recipients

If your organization has existing user accounts in an on-premises Active Directory environment, you can synchronize those accounts to Azure Active Directory in the cloud. Using directory synchronization is recommended. To learn more about the benefits of using directory synchronization, and the steps for setting it up, see Manage mail users in EOP.

We empower security admins to customize their security settings to satisfy the needs of their organization. Although, as a general rule, there are two security levels in EOP and Microsoft Defender for Office 365 that we recommend: Standard and Strict. These settings are listed in the Recommended settings for EOP and Microsoft Defender for Office 365 security.

Miscellaneous/non-policy settings

These settings cover a range of features that are outside of security policies.



Security feature name Standard Strict Comment
Set up SPF to help prevent spoofing Yes Yes
Use DKIM to validate outbound email sent from your custom domain in Office 365 Yes Yes
Use DMARC to validate email in Office 365 Yes Yes Use action=quarantine for Standard, and action=reject for Strict.
Deploy the Report Message add-in or the Report Phishing add-in to improve end-user reporting of suspicious email Yes Yes
Schedule Malware and Spam Reports Yes Yes
Auto-forwarding to external domains should be disallowed or monitored Yes Yes
Unified Auditing should be enabled Yes Yes
IMAP connectivity to mailbox Disabled Disabled
POP connectivity to mailbox Disabled Disabled
Authenticated SMTP submission Disabled Disabled Authenticated client SMTP submission (also known as client SMTP submission or SMTP AUTH) is required for POP3 and IMAP4 clients and applications and devices that generate and send email.

For instructions to enable and disable SMTP AUTH globally or selectively, see Enable or disable authenticated client SMTP submission in Exchange Online.

EWS connectivity to mailbox Disabled Disabled Outlook uses Exchange Web Services for free/busy, out-of-office settings, and calendar sharing. If you can't disable EWS globally, you have the following options:

The Report message add-in and the Report phishing add-in uses REST by default in supported environments, but will fall back to EWS if REST isn't available. The supported environments that use REST are:

  • Exchange Online
  • Exchange 2019 or Exchange 2016
  • Current Outlook for Windows from a Microsoft 365 subscription or one-time purchase Outlook 2019.
  • Current Outlook for Mac from a Microsoft 365 subscription or one-time purchase Outlook for Mac 2016 or later.
  • Outlook for iOS and Android
  • Outlook on the web
PowerShell connectivity Disabled Disabled Available for mailbox users or mail users (user objects returned by the Get-User cmdlet).
Use spoof intelligence to add senders to your allow list Yes Yes
Directory-Based Edge Blocking (DBEB) Enabled Enabled Domain Type = Authoritative
Set up multi-factor authentication for all admin accounts Enabled Enabled

Troubleshooting

Troubleshoot general issues and trends by using the reports in the admin center. Find single point specific data about a message by using the message trace tool. Learn more about reporting at Reporting and message trace in Exchange Online Protection. Learn more about the message trace tool at Message trace in the Security & Compliance Center.

Report false positives and false negatives to Microsoft

To help improve spam filtering in the service for everyone, you should report false positives (good email marked as bad) and false negatives (bad email allowed) to Microsoft for analysis. For more information, see Report messages and files to Microsoft.

Create mail flow rules

Create mail flow rules (also known as transport rules) or custom filters to meet your business needs.

When you deploy a new rule to production, select one of the test modes first to see the effect of the rule. Once you are satisfied that the rule is working in the manner intended, change the rule mode to Enforce.

When you deploy new rules, consider adding the additional action of Generate Incident Report to monitor the rule in action.

In hybrid environments where your organization includes both on-premises Exchange and Exchange Online, consider the conditions that you use in mail flow rules. If you want the rules to apply to the entire organization, be sure to use conditions that are available in both on-premises Exchange and in Exchange Online. While most conditions are available in both environments, there are a few that are only available in one environment or the other. Learn more at Mail flow rules (transport rules) in Exchange Online.