The complete Outlook 365 signature setup — New Outlook, classic desktop, web, Mac, and mobile — plus why saving it once doesn't cover every device.
The MailSigCraft Team
MailSigCraft
Searching "how to add signature in Outlook 365" usually starts with one honest assumption: that Outlook is one product, and setting a signature once will make it show up everywhere you send mail. It won't. "Outlook 365" is a Microsoft 365 subscription that unlocks five genuinely separate apps — New Outlook for Windows, classic Outlook for Windows, Outlook on the web, Outlook for Mac, and Outlook mobile — and four of them keep their own independent signature setting. This guide walks through the exact menu path for each one, then explains why they don't sync by default and what actually makes them sync when they can.
Most people land here from New Outlook for Windows or a browser tab at outlook.office.com — the two share a signature store, so one setup covers both.
Open the MailSigCraft editor, pick a template, fill in your details, and click Copy Signature.
Click the gear icon in the top-right corner, then Mail → Compose and reply (in Outlook on the web, click "View all Outlook settings" at the bottom of the panel first).
Click + New signature, name it, then click inside the editor box and paste (Ctrl+V or Cmd+V).
Use the For new messages and For replies/forwards dropdowns to assign your new signature to both, then click Save.
That covers New Outlook and Outlook on the web. If you also use classic Outlook for Windows, Outlook for Mac, or the mobile app, each needs its own pass — the picker below gives you the exact path for whichever one you're staring at right now.
How to tell: Rounded top toolbar, a left-hand app rail with icons for Mail/Calendar/People, and a toggle at top-right that says “Try the new Outlook” (already on).
New Outlook and Outlook on the web read from the same cloud-stored signature, so this step covers both if you use New Outlook as your main client.
Based on Microsoft's published menu paths for each Outlook 365 surface as of mid-2026. Not a live check of your tenant — a reliability read on which store you're editing.
Outlook's signature architecture wasn't designed as five apps sharing one setting — it grew that way as Microsoft rebuilt the product over a decade, and the storage locations never fully converged.
This is the single most common report. You add a signature in Outlook on the web, send yourself a test, and it looks perfect — then classic Outlook for Windows on the same machine shows nothing, or shows an old signature.
Classic Outlook keeps its own signature files unless roaming signatures is enabled. Check File → Options → Mail → Signatures for a local copy, and separately confirm your mailbox is Microsoft 365 or Outlook.com (roaming signatures does not work on Exchange on-premises or IMAP/POP accounts) before expecting the cloud version to appear automatically.
Microsoft requires classic Outlook to be on a recent monthly-channel build (2303 or newer) for roaming signatures to activate at all. On an older or slowly-updated build, the feature silently does nothing — no error, the signature just never appears.
Check your build under File → Office Account → About Outlook, and confirm "Store my Outlook settings in the cloud" is turned on under File → Options → General. Then fully sign out and back into the affected client — roaming signatures pulls on a fresh sign-in, not a background refresh. The Outlook sync deep-dive covers every branch of this diagnosis.
Outlook mobile has never participated in roaming signatures, regardless of account type or build. Whatever is set under Settings → [account] → Signature in the app is entirely local to that device.
Set the mobile signature separately, and expect it to be simpler — the mobile editor supports basic formatting (bold, italic, links) but will mangle a heavy, table-based HTML signature pasted in from desktop. Keep the mobile version short.
If you copy from a signature generator and paste with Ctrl+Shift+V (or your browser strips formatting on copy), Outlook inserts plain text instead of the styled HTML. This looks like a signature-tool bug but is actually a paste-method issue.
Use a plain Ctrl+V (or Cmd+V on Mac) inside the signature editor box specifically — not inside the compose window, and not with a "paste as text" shortcut. MailSigCraft's Copy Signature button copies rich HTML to the clipboard; a plain-paste shortcut discards that on the way in.
Every one of the five surfaces has two separate default dropdowns — one for new messages, one for replies and forwards — and several of them default the reply slot to "None."
Re-open the signature settings for that specific surface and confirm both dropdowns point at the same signature. This has to be checked per surface; setting it correctly in Outlook on the web does not fix the reply default in classic Outlook.
The confusion starts with the name itself. A Microsoft 365 subscription doesn't ship one Outlook — it entitles you to install and sign into any of the five clients above, on any device, and Microsoft has been actively steering desktop users from classic Outlook toward New Outlook for several release cycles now. That migration is exactly why so many people land on this search: they set a signature in whichever Outlook they used yesterday, then open a different one today and find it blank.
Most people who search this keyword are moving between exactly these two, since Microsoft is actively migrating users from classic to New Outlook.
Signature lives in your Microsoft 365 mailbox. Setup takes under 2 minutes, and it's the same setting whether you're in the app or the browser. No local files, nothing to back up.
Signature is a local file by default, with roaming signatures as an opt-in bridge to the cloud store — gated on account type (Microsoft 365 / Outlook.com only) and a minimum build (2303+). Until both conditions are met, treat it as a separate setup.
No roaming-signatures support at all, on any account type or build. The Mac client's signature editor is also more limited than Windows — some inline CSS from a desktop-authored signature can render differently, so paste-test after setup.
If you send from four or five of these surfaces regularly, budget ten minutes total rather than expecting one setup pass to cover everything — that's the realistic time cost of Outlook 365's split signature architecture.
Identify every Outlook surface you actually send from — New Outlook, classic desktop, web, Mac, mobile. Most people use 2–3, not all 5.
Set the signature on each one individually, using the picker above for the exact menu path.
Confirm both dropdowns (new messages, replies/forwards) on every surface — this is the #1 "it randomly stopped working" report.
If you rely on roaming signatures, verify the build number and cloud-settings toggle rather than assuming it's active.
Only between New Outlook and Outlook on the web, which share one cloud store by default. Classic Outlook for Windows needs roaming signatures explicitly enabled (Microsoft 365/Outlook.com mailbox, build 2303+). Mac and mobile never sync automatically from any surface.
Feature updates occasionally reset the "For replies/forwards" dropdown to "None" even when "For new messages" survives. Re-check both dropdowns after any Outlook update.
Each account (and each send-as alias) gets its own signature slot inside the same client. You can paste the identical HTML into multiple slots, but there's no single "apply to all accounts" toggle.
Only basic rich text (bold, italic, links, and simple images added through the app's own tools) — a full table-based HTML signature pasted from desktop typically loses its layout on mobile.
No. Outlook for Mac maintains its own local signature store with no roaming-signatures support, so it always needs to be set up separately regardless of account type or build.
Not automatically. New Outlook reads from the cloud signature store, while classic Outlook's default signature is a local file. If you never turned on roaming signatures beforehand, re-create the signature once inside New Outlook using the steps above — it only takes the one pass, and from then on it's shared with Outlook on the web too.
"Outlook 365" isn't one signature setting — it's up to five, and only two of them (New Outlook and Outlook on the web) share a store by default. Set the signature on every surface you actually send from, double-check both the new-message and reply/forward defaults on each one, and treat roaming signatures as a bonus that requires the right build and account type — not a guarantee.
Same story as Mac — always local, never synced. Because the mobile editor only exposes basic rich text, keep the mobile signature short and treat it as a simplified version of the desktop one rather than an identical copy.
Send a real test email to a second address and open it from each client you use, not just the one you edited in.