The New Outlook becomes mandatory: what SMEs need to do with the classic version

Anyone who has opened Outlook on Windows recently has probably seen the toggle: 'Try the new Outlook'. What started as an optional preview has become an irreversible direction. Microsoft confirmed the timeline in early 2026: for commercial Microsoft 365 customers, classic Outlook for Windows is being phased out in 2026, with a definitive end of mainstream support late in the year.

For SMEs this means waiting is no longer an option. Plan now and the migration is calm. Leave it and you will face it at an inconvenient moment with rushed rollouts and confused staff.

What is different about the New Outlook?

The New Outlook is essentially the Outlook web version wrapped in a desktop app. Under the hood it is the same as Outlook.com and the version in your browser. That has three consequences.

First, all data lives in the cloud. Local .ost and .pst files largely disappear, with a few limited exceptions. For most users that is fine because the mailbox is the same everywhere, but for organisations storing archives in local .pst files this needs attention.

Second, COM add-ins no longer work. Classic Outlook supported plugins such as older CRM integrations, Adobe Sign extensions and special accounting add-ons. The New Outlook only works with the modern Outlook add-in standard. Modern variants exist for most popular tools, but legacy systems can cause problems.

Third, the user interface is consistent with Outlook on web and mobile, with faster updates for new features such as Copilot integration, meeting intelligence and collaboration features from Loop and Teams.

What does not yet work, or works differently?

The New Outlook has matured in 2026, but rough edges remain. Advanced rules and macros are more limited. Some offline scenarios are less extensive than in the classic version. PST import is possible but more cumbersome. For specific professions, such as finance teams making intensive use of Outlook categories, tasks and quick steps, friction can occur.

Which deadlines apply?

Three dates to remember. From January 2026, the New Outlook is already the default for new Microsoft 365 installations. From mid-2026, classic Outlook installations via Microsoft 365 are actively blocked for new users. End of 2026, mainstream support for classic Outlook for Windows ends for commercial Microsoft 365 customers. After that, only critical security updates follow for a limited period.

How do you approach the migration?

Five steps for a structured transition.

Step 1: inventory which add-ins and integrations your organisation uses in Outlook. CRM, e-signatures, accounting integrations, template tools. Check per vendor whether a modern Outlook add-in is available, or whether they are still working on one.

Step 2: inventory .pst archives. Which users have large local archives? Plan the migration to online archive mailboxes or Microsoft 365 Backup as covered in earlier articles.

Step 3: choose a pilot group of five to ten users. Preferably from different roles: a sales role, an administrative employee, a management role. Have them actively use the New Outlook and gather pain points.

Step 4: communicate to the broader organisation. A short instructional video, a list of what is different, and clarity on when everyone migrates. Surprise is the biggest enemy of adoption.

Step 5: roll out in phases by team or department. Keep a fallback path open for the first weeks, and plan an evaluation moment after a month.

When to start?

For most SMEs, May to September 2026 is the ideal window. You still have time to plan calmly, you avoid the busy year-end closure in November and December, and you are ready before year-end without rushing.

Want guidance on the migration plan, employee communications or the technical roll-out of the New Outlook in your organisation? Zarioh helps SMEs with the complete Microsoft 365 environment. Contact us for a no-obligation conversation.