Removing Duplicate Contacts From Outlook’s View

When Microsoft published message center notification MC835643 (last updated 12 September 2024), I was a little confused (a more normal state for me than you might imagine) and wondered how well the new contact duplication feature would work. Now that the feature has reached my tenant, it’s pretty obvious what happens. Let me explain.

The Problem with Personal Contacts

First, a comment about personal contacts: they’re easy to mess up over years of acquiring business cards from people or details scrawled on convenient pieces of paper, or just by making a mistake when importing contacts from an external source (like this example). Microsoft’s suggested resolution for a mess of duplicates by exporting, pruning, and importing is viable but painful, which is why so many third-party products exist to maintain Outlook contacts.

Outlook (classic) does its best to stop duplicate contacts by highlighting potential problems when a user attempts to add a new contact (Figure 1). I can’t say when Outlook (classic) started to do this. All I know is that I have accrued some duplicate contacts over the years.

The other problem with personal contacts is that their accuracy degrades over time as the people the contacts describe move jobs, locations, or otherwise change. There’s not a lot you can do about this issue short of maintaining a hawk-like eye over LinkedIn updates to detect changes in peoples’ circumstances to allow you to update your contacts. The summary is that lots of user mailboxes include duplicate contacts.

Hiding Duplicate Contacts

The new Outlook for Windows and OWA aim to reduce the visibility of duplicate contacts by detecting and hiding contacts “that are exact duplicates or proper subsets of other contacts. This means that if you have multiple entries for the same person, Outlook will consolidate them, keeping only the most complete contact visible.” Hiding potential duplicates leaves them in the Contacts folder of your mailbox and visible through other clients like Outlook (classic) and Outlook mobile.

There’s no administrative control over the feature to enable or disable it on a per-user or tenant-wide level. It’s now how the new Outlook and OWA clients work.

To detect duplicate contacts, Outlook looks for clues. Finding contacts that are perfect replicas of each other is the easiest way to detect duplicates. After that, looking for the same details such as email address, work phone, and so on build a case to hide contacts as duplicates by satisfying the requirement that contacts are a proper subset of the others.

Explaining a mathematical concept to end users who want to know why duplicate contacts disappear from view can be challenging. I can’t track down support documentation that might explain what happens in plain English.

When everything works, duplicates contacts disappear from view. Figure 2 shows that only one of the two contacts for Larry Hawkes is shown.

After the initial flush of success, some questions arise. How did Outlook decide to show one contact and not the other? Is it based on completeness of contact properties, or the last time the contact was modified (on the basis that the latest contact information is likely the most accurate).

Then I added another contact for Larry Hawkes (with the same email address and roughly the same contact properties). After refreshing Outlook, the three contacts were visible (Figure 3).

Perhaps the thought was that while people are likely to have duplicates, having three contacts that refer to the same person is outside the boundaries of what Outlook can resolve. If so, Microsoft should document this.

Here’s the contact information visible with PowerShell:

Get-MgUserContact -UserId $User.Id -Filter “Companyname eq ‘Contoso'” | Format-Table displayname, companyname, emailaddresses, businessphones

DisplayName CompanyName EmailAddresses BusinessPhones
———– ———– ————– ————–
Larry Hawkes Contoso {Larry.Hawkes@contoso.com} {+1 (206) 177 1931}
Larry Hawkes Contoso {Larry.Hawkes@contoso.com} {+1 (206) 177 1931}
Larry Hawkes Contoso {Larry.Hawkes@contoso.com} {+1 (206) 177 1931}

I expect three contacts with the same email address, display name, company name, and work phone number to be called as duplicates, and I think most other people would too.

The problem might be to do with timing, Perhaps once Outlook resolves duplicates, it doesn’t go back and check again for a set period. The client certainly doesn’t perform a check on startup because I tried that several times. Microsoft hasn’t said if Outlook uses a schedule to decide when to check for duplicates or if a user can request a check (for instance, after importing some contacts from an external source).

Improvement Needed

Don’t get me wrong. I like the idea of hiding duplicate contacts. It’s a good thing to do. It’s just that it would be better if Microsoft delivered better documentation and some controls for administrators and users to dictate how the feature works instead of assuming that everyone will be happy with the code as delivered.

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