How to Use Microsoft 365 MailTips to Improve Email Performance

When a user begins composing an email, Outlook queries the Exchange server to check for conditions that trigger MailTips. If any conditions are met, a notification appears instantly. These alerts are designed to be helpful and informative. For instance, a mailtip might be established to warn a user if a file attachment would cause the email to exceed email size limits. 

Common MailTips Include:

• Message size limit warnings
• Notice that a colleague has configured Automatic Out-of-Office replies
• Warning of Large distribution list in send:, cc:, and bcc: fields
• Restricted recipients

Configuring Microsoft 365 mailtips like these help users make smarter decisions before sending emails.

MailTips do not scan email content for sensitive data like credit card numbers. For that, use:

• Data Loss Prevention (DLP): Detects and blocks sensitive content.
• Sensitivity Labels: Automatically classify and protect emails.

For example, in situation where it is inappropriate to include a full length credit card number in an email, conditions can be configured to automatically obscure all but a few numbers of the card as the server processes the outgoing email, ask the sender to edit the email, or block the email. In this way, Exchange Online can activeley monitor email traffic to help a business control personal data that might lead to loss ofr damage to customers. These utilities are especially useful in financial services and medicine.

DLP and Sensitivity labels are subject to adequate Microsoft 365 licensing – please ask if you need more information.

Microsoft 365 allows admins to configure MailTips that warn users when their email might exceed the organization’s size limits. While the maximum message size can be set up to 150 MB, the default is often 25 MB or 35 MB, depending on your configuration. In theory, Microsoft 365 can handle large attachments. However, this causes problems for server storage at scale, and large emails are often dropped by external servers as they pass to recipients. For large files, use file sharing with links to files stored in OneDrive and Sharepoint.

Use this workflow to establish a custom Mailtip to warn users about large attachments:

Step-by-Step Guide Using Exchange Admin Center (EAC)

1. Log in to the Exchange Admin Center\ Navigate to https://admin.exchange.microsoft.com and sign in with your admin credentials.
2. Go to Recipients > Mailboxes\ Select the mailbox you want to configure.
3. Open Mailbox Properties\ Click the mailbox name to open its details pane.
4. Navigate to Others > Manage MailTip\ In the flyout panel, find the Manage mail tip option.
5. Enter Your Custom MailTip\ Example:\ “Warning: This mailbox has a 25 MB attachment limit. Large files may cause delivery failure.”
6. Save Changes\ Click Save to apply the MailTip.

!!! Note: MailTips are limited to 175 characters and support basic HTML formatting.

Optional: Use PowerShell for Bulk Configuration

If you need to handle several email accounts, it is easier to do this using Powershell to perform a batch operation. Powershell can be used to manage this indivdually, too. Powershell is beyond the scope of this article, and if you need help with Powershell, please contact us.

Microsoft 365 MailTips helps prevent email errors and improves communication. By configuring Microsoft 365 MailTips—especially for common issues like large attachments—admins can reduce support tickets, avoid non-delivery reports, and maintain a professional email environment.

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