Email Signature for Outlook 365 / Microsoft 365

Classic Outlook (also called 'Outlook Desktop' or 'legacy Outlook') is the traditional Windows application that uses Microsoft Word as its email rendering engine — this is why HTML signatures often break in it. Outlook 365 (also called 'New Outlook for Windows') is a newer version that Microsoft began rolling out in 2023 and is now default for many Microsoft 365 subscribers. New Outlook uses a web-based rendering engine, so HTML signatures behave much more like they do in Outlook Web Access. The installation steps are different for each version.

Classic Outlook has a 'File' menu in the top-left corner of the window, like a traditional Office application. New Outlook looks more like a web app — there's a gear/settings icon in the top-right corner, and it lacks the classic ribbon in the same form. You can also check: in classic Outlook, go to File → Office Account and check the version number. New Outlook version numbers are typically much higher (16.x+) and the interface is noticeably different.

Yes. There are two approaches. First, Exchange Transport Rules (ETR) — admins can create rules in the Exchange Admin Center that append a disclaimer or signature to all outgoing emails server-side. This doesn't appear in the user's compose window but attaches after sending. Second, Microsoft 365 supports 'roaming signatures' — a feature that syncs signature settings across devices for a user. For company-wide managed signatures with more control, third-party tools like Exclaimer or Opensense integrate with Microsoft 365 and offer per-user field population (e.g., pulling name and title from Azure AD).

Roaming signatures is a Microsoft 365 feature that stores your Outlook signatures in your Exchange Online mailbox rather than locally on your device. This means if you sign into Outlook on a new computer, your signatures are already there. It requires Microsoft 365 Exchange Online (not on-premises Exchange) and Outlook for Windows 16.0.14326.20000 or later, or New Outlook. When enabled, signatures appear in Outlook Web App and sync to Outlook Desktop automatically.

Classic Outlook uses Microsoft Word's HTML rendering engine, which does not support modern CSS (flexbox, grid, media queries, etc.) or many HTML5 features. Table-based layouts — using HTML <table> elements for positioning — are the reliable format. CSS float, position: absolute, and most CSS layout techniques break. NeatStamp generates table-based HTML specifically to work in classic Outlook. If you're writing HTML yourself, use tables and inline styles only.

Open the Outlook app, tap your profile photo or initials in the upper left, tap Settings (gear icon), scroll to 'Email Signature', toggle it on, and edit. Note: the Outlook mobile signature is plain text only. For HTML signatures on mobile, set up your signature in Outlook Web (outlook.office.com) — Outlook mobile will then pull from that setting in some configurations, though behavior varies. Testing on your specific device is recommended.

Microsoft doesn't publish a strict character limit for Outlook signatures, but practical performance degrades above 100KB of HTML. For images, keep each image under 100KB and your total signature size under 200KB. Very large signatures can trigger spam filters on receiving servers and slow down email loading. Keep image dimensions reasonable: logo at 120–180px wide, headshot at 80–100px.