How to Manage Recipient Limits for Exchange Online Mailboxes

Recipient limits of Exchange Online mailbox define the maximum number of recipients (To, CC, and BCC) a user can include in a single email. These limits are in place to maintain service reliability and enhance security. However, some admins may need to set custom recipient limits for Exchange Online mailboxes to meet specific organizational needs.

For instance, increasing the limit might be necessary for mailboxes that frequently send emails to large distribution lists. Conversely, reducing the limit for a mailbox can help mitigate the risk of spam emails being sent to a broader audience in the event of a compromised account.

In this blog, let’s explore the possible configurations to set custom recipient limits in Exchange Online mailboxes.

By default, the recipient limit is configured as 500 for all mailboxes created in the organization. This value is defined by the mailbox plan assigned during mailbox creation and is consistent across all new mailboxes unless explicitly changed.

The maximum number of email recipients can be modified by customizing the recipient limit of existing mailboxes or new mailboxes that will be created in the future.

Regardless of the plan type (business, enterprise, or others), the recipient limit can be customized up to 1000 recipients per email. However, for encrypted messages, the maximum recipient limit is set to 200 recipients.

Since January 2020, admins have been able to customize the Exchange Online recipient limit. This limit can be set between 1 and 1,000 either through PowerShell or the Exchange Admin Center. While PowerShell offers a full range of customization options, a subset of these features is available in the Exchange admin center.

Note: Using PowerShell, you can also set a mailbox’s recipient limit to “Unlimited”, which enforces the tenant-wide recipient limit for that mailbox.

Let’s explore the various scenarios to manage recipient limits of Exchange Online mailboxes.

• Configure recipient limits of all users in Exchange Online
• Set a custom recipient limit on an Exchange Online mailbox
• Customize recipient limit for multiple mailboxes in Microsoft 365
• Manage the custom recipient limit for a specific department
• Set recipient limit for new mailboxes created in the future

Before configuring, connect to the Exchange Online PowerShell module and review the recipient limit of all mailboxes using the below cmdlet. This helps to determine the appropriate limit needed for the mailbox.

Get-mailbox -ResultSize Unlimited | Select-Object DisplayName, UserPrincipalName, RecipientLimits

If your organization needs a consistent recipient limit for all users, you can configure it across all mailboxes. Setting a uniform recipient limit for outgoing email messages across all mailboxes ensures consistency and simplifies policy enforcement.

Using Exchange Admin Center

1. Navigate to the Mailboxes page in the Exchange admin center.
2. Select all mailboxes by clicking the checkbox available in the header, then click Set recipient limit in the toolbar.
3. If the option is invisible, click the ellipsis (…) and select it from the dropdown.
4. Specify the maximum number of recipients for the mailbox in the Maximum recipients box and Click Save.

Using Exchange Online PowerShell

Run the below cmdlet to set the recipient limits for all users in Office 365.

Get-Mailbox -ResultSize Unlimited | Set-Mailbox -RecipientLimits <RecipientLimitValue>

Replace <RecipientLimitValue> with any value between 1 and 1,000 or Unlimited based on your requirements.

Customizing the recipient limit for an Exchange Online mailbox is crucial for managing specific scenarios. Limiting the maximum number of recipients for outgoing emails helps prevent the spread of malicious emails, especially in mailboxes showing signs of compromise such as risky sign-ins or multiple failed login attempts. Conversely, increasing the limit is useful for users who need to communicate with larger audiences, such as managers or project leads.

Using Exchange Admin Center

1. Navigate to the Mailboxes page and select the mailbox you wish to customize the recipient limit.
2. Go to the Others tab and select Set recipient limit under Recipient limit.
3. Enter the maximum number of recipients for the Exchange Online mailbox and click Save.

Using Exchange Online PowerShell

Run the below cmdlet to set a custom recipient limit for a specific Exchange Online mailbox.

Set-Mailbox <MailboxUPN> -RecipientLimits <RecipientLimitValue>

Here, replace <MailboxUPN> with the User Principal Name of the mailbox and <RecipientLimitValue> with the desired recipient limit.

Imagine a scenario where a list of users in your organization needs a higher recipient limit for tasks like sending end-of-month billing statements or performance reports. Here, managing the recipient limit for those mailboxes individually can be a tedious and time-consuming task. To address this, you can set custom recipient limits in bulk.

Using Exchange Admin Center

1. Select the mailboxes you want to manage on the Mailboxes page.
2. Click Set recipient limit on the top of the page.
3. Specify the maximum number of recipients limit and click Save.

Using Exchange Online PowerShell

To set a custom recipient limit for bulk users, first create a CSV file containing the users’ UPNs as shown below.

Then, execute the following cmdlet to set the recipient limit for multiple mailboxes simultaneously.

Import-Csv "<FilePath>" | ForEach-Object { Set-Mailbox $_.UserPrincipalName -RecipientLimits <RecipientLimitValue> }

Here, replace <FilePath> with the path to your CSV file and <RecipientLimitValue> with a value based on your requirements.

In many organizations, departments like Finance and HR often need higher recipient limit for outgoing emails compared to other users. In such cases, you can set a custom limit for the specific department to meet their communication needs while maintaining consistency.

This configuration can only be done through PowerShell, as filtering the user based on the departments is not possible in the Exchange admin center.

Run the following cmdlet to configure the recipient limit of all mailboxes in a specific department.

Get-Mailbox -ResultSize Unlimited -Filter {Department -eq "<DepartmentName>"} | Set-Mailbox -RecipientLimits <RecipientLimitValue>

Replace <DepartmentName> with the name of the department and <RecipientLimitValue> with your desired limit.

By default, newly created mailboxes in Exchange Online are assigned a recipient limit of 500. To modify this, you’ll need to update the mailbox property of each new mailbox. However, to simplify this process, you can define a new default recipient limit for all future mailboxes in your organization, with values between 1 and 1,000. Sounds interesting, right? Let’s dive into how to set it up!

The recipient limit is applied to all new mailboxes based on the organization configuration assigned to the chosen mailbox plan. To change this, understanding the available plans and the default recipient limits associated with them is essential. To do so, use the following cmdlet.

Get-MailboxPlan -ResultSize Unlimited | Select-Object Name, RecipientLimits

Then, run the below PowerShell cmdlet with the specific plan you need to set the new default recipient limit.

Get-MailboxPlan <MailboxPlanName> | Set-MailboxPlan -RecipientLimits <RecipientLimitValue>

Replace the <MailboxPlanName> with the desired plan and <RecipientLimitValue> with the new default recipient limit value. After executing the cmdlet, when you assign the specified plan to a user, they will inherit the new default recipient limit value.

To customize the default recipient limit for all Exchange Online mailbox plans in your organization, run the below PowerShell cmdlet.

Get-MailboxPlan -ResultSize Unlimited | Set-MailboxPlan -RecipientLimits <RecipientlimitValue>

The tenant-level recipient limit applies across all mailboxes in the tenant, but it only takes effect when the mailbox recipient limit is set to unlimited.

Run the below cmdlet in Exchange Online PowerShell to set the tenant-level recipient limits.

Set-TransportConfig -MaxRecipientEnvelopeLimit <RecipientLimitValue>

Don’t forget to replace <RecipientLimitValue> with your preferred tenant-level recipient limit.

• If you set the recipient limit of a mailbox and tenant level to any numeric value between 1 and 1,000, the mailbox setting takes priority, because it has a numeric value, which overrides the tenant setting.
• If you set the mailbox recipient limit to unlimited and the tenant-level limit to a numeric value, the tenant-level limit will override the mailbox setting, as the mailbox value is not numeric.

Now, you might be wondering, what if both the mailbox and tenant-level recipient limits are set to unlimited? The answer is simple: both being set to unlimited effectively means you’re giving the mailbox the maximum recipient limit of 1,000!

For a better understanding, refer to the table below.

Mailbox Recipient Limit (Set-Mailbox)	Tenant-level Recipient Limit (Set-TransportConfig)	Behavior	Explanation
100	400	The mailbox can send emails to up to 100 recipients.	The tenant-level setting is ignored because the mailbox setting has a numeric value.
700	50	The mailbox can send emails to up to 700 recipients.	Since the mailbox setting is a numeric value, the tenant-level setting for this mailbox is ignored. (Even though it’s more restrictive than the mailbox setting)
Unlimited	200	The mailbox can send emails to up to 200 recipients per email.	Here, the mailbox setting is ignored because the tenant-level setting applies when the mailbox setting is unlimited.
Unlimited	Unlimited	The mailbox can send email to up to 1000 recipients.	Since both settings are unlimited, the maximum recipient limit is applied.

Points to Remember:

• A distribution group that is stored in the organization’s shared address book counts as one recipient. In contrast, each recipient in a personal distribution list is counted separately.
• Even if your Exchange Online recipient rate limit allows 10,000 recipients per day, you cannot send more than 1,000 recipients in a single email. This is because the maximum recipient limit in Office 365 for a single mail is 1,000.
• If the number of recipients exceeds the limit, the message is rejected, and the sender receives a bounce error: 550 5.5.3 RESOLVER.ADR.RecipLimit; too many recipients.
• The recipient limit includes both internal and external recipients.
• While the recipient limit controls the number of recipients per email, you can also restrict the number of recipients per hour using the outbound spam policy. So, even if you sent emails within the recipient limit, you could run into errors if you exceed the hourly threshold set by the policy.

I hope this blog has helped you understand how to easily set custom recipient limits for your Exchange Online mailboxes. Feel free to reach out in the comments if you have any questions or need further assistance!