Who this is for. Practice managers, partners and internal IT people at firms that run a practice management or document management system beside Microsoft 365. It applies whichever product you use.
Boundaries. We name no products and claim no expertise in any of them. The Microsoft details were checked against Microsoft Learn in October 2026 and are listed under Sources. Your vendor's documentation and support agreement take precedence for anything about its product.
1. Who is responsible for what
Most integration faults sit between two parties, and each can fairly say the problem is on the other side. Agreeing who owns what, before anything breaks, shortens every fault.
| Area | Usually the vendor | Usually the IT provider | Usually the firm |
|---|---|---|---|
| The application and its updates | Builds, supports and releases updates | Installs or deploys them on an agreed schedule | Decides when to take a major version |
| Outlook and Word add-ins | Supports the add-in and states which Office versions it works with | Deploys it, keeps Office on a supported version, reports faults | Shows staff how to use it |
| Hosted matter data | Hosting, backups and restores, when the vendor hosts the system | Records the vendor's backup arrangements | Owns the contract and the data |
| Sign-in and accounts | Supports the sign-in methods the product offers | Manages Microsoft 365 identities, MFA and Conditional Access | Approves who gets access |
| Devices and network | Publishes minimum requirements | Keeps devices, network and internet within them | Funds replacements |
"Usually" matters here. Contracts differ, and the vendor's support agreement is what decides. Keep a copy where the firm can find it.
2. Email filing
Filing email to a matter is where most firms feel integration problems first. It usually works through an add-in in Outlook, a connection to the mailbox, or both. Things to check:
- which accounts the filing covers, including shared mailboxes such as reception or accounts;
- whether filing works the same in Outlook on the desktop, Outlook on the web and on phones, or only on the desktop;
- what happens to the mailbox copy after filing, and whether Microsoft 365 retention settings agree with that;
- how staff find filed mail if the add-in stops working for a day.
The new Outlook for Windows
People using Outlook on Windows can switch from classic Outlook to the new Outlook for Windows. Microsoft's developer documentation says VSTO and COM add-ins aren't supported in the new Outlook and have to be rebuilt as Outlook web add-ins, while classic Outlook still supports them. Before anyone at the firm switches, ask the vendor which kind its add-in is and whether a web add-in version exists.
3. Add-ins in Word and Outlook
Add-ins load inside Office, so an Office update can change how they behave without anyone touching the practice system. Ways to reduce surprises:
- Keep a list of every add-in the firm relies on, who supplies it and which Office versions the supplier supports. It belongs in the documentation register.
- Deploy add-ins centrally where the add-in allows it. Administrators can deploy Office add-ins to users and groups from the Microsoft 365 admin center, and Microsoft recommends a staged rollout: a small group first, then more people, then everyone.
- Stop people installing their own copies. Several versions of one add-in across different laptops make faults hard to trace.
4. Sign-in
Practice systems sign people in in different ways. Some use the person's Microsoft 365 account; others keep separate usernames and passwords. Each choice has consequences:
- Microsoft 365 sign-in. The firm's MFA and Conditional Access rules apply, and disabling a leaver's Microsoft 365 account usually ends their access in one step.
- Separate credentials. Leavers have to be removed in the practice system as well, and its own password and MFA settings need checking.
- Older connection methods. We block legacy authentication in Microsoft 365 for every client, because it can bypass MFA. An integration that still uses an older method to reach mailboxes will stop when that happens, so ask the vendor beforehand and test.
- Integration accounts. Some integrations use a dedicated account to read mailboxes or calendars. Record what each one can reach, who owns it, and how its password or secret is changed.
5. Updates
Three update cycles meet on every lawyer's laptop: Windows, the Microsoft 365 apps, and the practice system with its add-ins. We patch Windows and Office on a schedule through Intune. The practice system runs to its own release timetable.
- Ask the vendor which Windows and Office versions it supports, and for notice before a release that changes the integration.
- Agree a window for major practice system upgrades that avoids month-end billing and known busy weeks.
- Try changes on a small group of willing users before the whole firm.
- Know how to roll back, or whom to call, if an update breaks something mid-morning.
6. Testing after changes
A ten-minute test after any change to Office, Windows, sign-in or the practice system catches most breakages before a fee earner does. Keep the script short enough that someone actually runs it:
- 6.1Open a matter. Sign in to the practice system and open a current matter.
- 6.2File an email. File one received and one sent email to that matter from Outlook.
- 6.3Draft and save. Create a document from a precedent, save it to the matter, close it and open it again.
- 6.4Search. Find the email and the document again from the practice system.
- 6.5Record time. Make a time entry, if the system records time.
- 6.6Scan and print. Scan a page to the matter and print a document from it.
- 6.7Work remotely. Repeat one or two steps away from the office, if lawyers work remotely.
Note who ran the test, when, and the result. We record every change we make in your documentation register, so when something does break, the most recent change is easy to find.
7. Vendor details to keep on file
- the customer or account number;
- the support contract level and its hours;
- how faults are logged: portal, email or phone;
- the people at the firm the vendor will accept requests from, and whether your IT provider is authorised to log faults for you;
- licence counts and the renewal date;
- where hosted data is kept, and the vendor's backup and restore arrangements;
- where the vendor posts outage notices.
If you change IT provider, these details should come with you. The IT handover checklist lists them alongside everything else to collect.
8. Where we fit
Vendor liaison is part of our monthly fee. We hold the account details for your internet provider, phone system and practice software vendors, log faults, chase them and tell you when they are fixed. We look after the Microsoft 365 setup, devices and network these systems depend on, and check the connection still works after changes we make.
We don't claim expertise in any particular practice or document management product, and this guide names none. How the product itself is configured stays with the vendor and the firm. More on this is on our practice systems and vendor management page.
9. Sources
The Microsoft features described in this guide were checked against these Microsoft Learn pages. Anything we could not confirm there has been left out.
- Develop Outlook add-ins for the new Outlook on Windows Microsoft Learn
- Deploy Office Add-ins in the Microsoft 365 admin center Microsoft Learn