MailTips: Useful Guidance for Good User Email Habits

Informational Text to Encourage Good Message Habits

First introduced in Exchange 2010, a MailTip is informational text displayed when a recipient is added to a message in Outlook desktop and OWA. Some MailTips are system-generated and you can’t affect the text they display, such as those generated when messages are addressed to moderated recipients or when a recipient’s mailbox is full (a situation more unusual in the cloud than on-premises given the size of Exchange Online mailboxes). Others are controlled through the organization configuration.

Office 365 tenants should consider how to best use MailTips to help guide end users and make sure that they don’t do something like create the basis of a reply-all email storm by inadvertently sending a message to a large distribution list (the reply-all protection in Exchange Online is really only good for tenants with more than 5,000 mailboxes).

How Outlook Desktop and OWA Use MailTips

Last year, I commented about some problems in how clients displayed MailTips. Things have settled down since and despite obvious differences between Outlook and OWA, the two implementations reflect the style of each client. Figure 1 shows MailTips in Outlook while Figure 2 shows the MailTips generated for the same set of recipients (a mixture of internal and external addresses) in OWA.

MailTips displayed by Outlook for Windows
Figure 1: MailTips displayed by Outlook for Windows

It’s obviously easy to display a single MailTip. As these screens show, the challenge is how to communicate as much information to users without overloading the interface.

  • Outlook displays a list of external recipients, which means that unwanted recipients can be removed with a single click. After more than one external recipient is added to a message, OWA hides the list and the user must use Show details to see and remove individual recipients. Displaying a MailTip to highlight external recipients is governed by the MailTipsExternalRecipientsTipsEnabled setting in the Exchange Online organization configuration.
  • The same approach is used to list internal recipients who have automatic replies set. Outlook lists the recipients; OWA forces the user to use Show details to reveal the information.
  • Outlook uses different colors for internal and external recipients.
  • Outlook tells the user if the message is going to more recipients than the threshold set in MailTipsLargeAudienceThreshold in the Exchange Online organization configuration (normally 25). OWA doesn’t show this information.
  • OWA does a better job of showing custom MailTips set for internal recipients. In Figure 1, we see Outlook displaying only one custom MailTip; in Figure 2, OWA reveals that four recipients have custom MailTips.
OWA displays MailTips
Figure 2: OWA displays MailTips

You can argue about which approach is better. The important thing is that both clients display MailTips to surface a lot of information about recipients to allow the sender to decide if they need to adjust the recipient list. They might realize that the information in the message shouldn’t go to external recipients, or that the distribution is too wide, or that some people won’t see time-critical information because they are on vacation.

These are all good reasons to use MailTips, even if new mechanisms are available in Office 365 to restrict access to sensitive information that weren’t as easy (or didn’t exist) in on-premises Exchange. For instance, any confidential message should be protected with a sensitivity label to encrypt the content and restrict access to people who have the right to view the material.

MailTips Not Used with Outlook Mobile

What’s not so good is that Outlook Mobile doesn’t display MailTips, except to indicate the presence of external recipients in a message (Figure 3). There are probably many reasons for this, such as the limited amount of screen real estate available to the client and the lack of support for MailTips in the Microsoft synchronization protocol linking Outlook Mobile to Exchange Online. At least Outlook Mobile can highlight external recipients and can protect confidential messages with sensitivity labels, neither of which feature is supported by mobile clients using the older Exchange ActiveSync protocol. Being able to use advanced features is one of the reasons underpinning Microsoft’s push for Exchange Online mailboxes to use Outlook Mobile.

Outlook Mobile (iOS) warns about external recipients
Figure 3: Outlook Mobile (iOS) warns about external recipients

Controlling MailTips

Several settings in the Exchange Online organization configuration control how clients see MailTips. Here are the values configured on my tenant:

The settings mean:

  • MailTipsAllTipsEnabled: Set to True to use MailTips.
  • MailTipsExternalRecipientsTipsEnabled: Set to True to have clients highlight messages addressed to external recipients.
  • MailTipsGroupMetricsEnabled: Set to True to have Exchange Online calculate the number of members in distribution lists. This data is used to establish if the large audience threshold is exceeded in messages. A background process checks distribution lists periodically, so don’t expect the numbers used to be 100% accurate.
  • MailTipsLargeAudienceThreshold: The default is 25. It’s lower here as a reminder that there might be a better way to share information with large audiences, such as a post in a Teams channel. Of course, if you don’t use Teams, you could increase the threshold right up to the maximum number of recipients an Exchange Online user can address in a message (1,000).
  • MailTipsMailboxSourcedTipsEnabled: Set to True to have Exchange Online look at mailbox data such as auto-reply messages to generate MailTips.

Custom MailTips

Custom MailTips are text of up to 175 characters assigned to any valid mail-enabled recipient type including mailboxes, shared mailboxes, group mailboxes, mail contacts, distribution lists, and dynamic distribution lists.

For example, these commands set custom MailTips for a mailbox, a Microsoft 365 group, and the mail user object created for a guest account:

You can also look for objects with custom MailTips. For instance, here’s how to do it for mailboxes:

As you can see., MailTips are stored in HTML format.

Users or the owners of distribution lists or groups cannot set MailTips unless they are an Exchange Online administrator and can update recipients with PowerShell. Like many mailbox settings, it takes a few hours before clients pick up MailTip changes.

Translated MailTips

Exchange Online operates in a multinational, multilingual environment. When you create a custom MailTip, it becomes the default for all languages. To create language-specific translations for a MailTip, you update the multi-valued MailTipTranslations property for an object. For example, this command sets up Spanish, French, and German translations for a mailbox. Clients configured in these languages display the language-specific value. If no value exists for the client language, the default MailTip is used.

To validate the translations, run a command like this:


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