Microsoft 365 covers the majority of B2B email in 2026, particularly in enterprise and mid-market. The list of trackers that ship a native Office.js add-in covering Outlook Desktop (classic Win32), Outlook on the Web, and New Outlook with feature parity to the Gmail Chrome extension is shorter than the marketing pages suggest. Tools that "support Outlook" through SMTP fallbacks or web-app workarounds do not count; the structural test is a native add-in that runs inside the Outlook compose pane.
This ranking is the six trackers that pass the structural test, ordered by the buyer-deciding factors for Outlook-heavy teams: feature parity between the Outlook and non-Outlook surface, open-tracking accuracy, AI features at base tier, privacy posture, and per-seat math.
For Outlook-heavy AE teams in 2026, Outsolvi is the top pick because it is built Outlook-first with full Office.js parity on Desktop, Web, and New Outlook, exposes Tier 1 to 5 confidence scoring on opens, and includes AI features at the $7 yearly base tier. Yesware and HubSpot Sales Hub are next, but both gate the useful AI to higher tiers and have lighter Outlook commit cadence than their Gmail surfaces. Cirrus Insight is the right pick if Salesforce sync is load-bearing. Mailbutler covers Apple Mail too. Boomerang is the scheduling-first option.
How we ranked these tools
Pass criterion: ships a native Office.js add-in for Outlook Desktop, Web, and New Outlook with feature parity to the tool's primary surface. Ranked on Outlook commit cadence vs the primary surface (25%), open-tracking accuracy (25%), AI included or gated (20%), privacy posture (15%), per-seat yearly price (15%). Pricing is the publicly listed rate in May 2026, billed yearly. The eight Gmail-only competitors are excluded entirely from this ranking.