Adding an email signature in Outlook sounds straightforward — open settings, paste in your signature, done. In practice, Outlook is the most complex email client to work with. The desktop version behaves differently from the web version, Mac differs from Windows, and HTML signatures that look perfect in Gmail can fall completely apart in Outlook 2016. This guide covers every version, every platform, and the reasons why it all works the way it does.
If you've ever pasted a beautiful HTML signature into Outlook only to watch it lose its formatting, strip your images, or squash everything into a plain-text mess — this is for you. Let's fix it properly.
Why Outlook Is Different from Gmail
Gmail renders your signature using a proper web browser engine — the same one that renders web pages. It understands modern CSS, respects flexbox, handles PNG transparency, and behaves predictably.
Outlook for Windows (the desktop version, 2007 through 2021) uses Microsoft Word as its HTML rendering engine. This is not a joke. When Outlook renders an HTML email, it is not running a browser — it is asking Word to interpret HTML, which it was never designed to do. Word strips or ignores flexbox, CSS grid, many border properties, percentage widths, and SVG images. Shadows disappear. Rounded corners vanish in some versions. Transitions do nothing.
The result: an email signature that looks polished in Gmail can look broken in Outlook unless it was built specifically to handle both renderers.
"Outlook for Windows uses Word as its HTML renderer — and Word was never designed to render email."
The solution, as email developers have known for years, is table-based HTML. Tables are the one layout system that Outlook has reliably supported since Outlook 2003. A signature built on a two-column table — photo on the left, contact details on the right — will render consistently across every Outlook version. Flexbox-based signatures will not.
Adding Your Signature in Outlook for Windows
These steps apply to Outlook 2016, 2019, 2021, and Microsoft 365 on Windows. The menu paths are nearly identical across all versions.
Open the Signatures settings
In the top menu, click File → Options → Mail → Signatures…. Alternatively, open a new email compose window and look for Insert → Signature → Signatures… in the ribbon. Either path takes you to the same dialog.
Create a new signature
Click New in the "Email Signature" tab. Give it a name — something like "Main" or "Professional." Click OK. You'll now see an editing area in the lower half of the dialog.
Paste your HTML signature
If your signature was built in a tool like Send Like a Pro or an external HTML editor, copy the formatted version (not the raw HTML code) and paste it directly into the signature editor box. The editor is WYSIWYG — paste formatted content, not HTML markup.
Set as default
In the top-right of the Signatures dialog, use the "New messages" and "Replies/forwards" dropdowns to assign your new signature. Select your signature name from both dropdowns. Click OK.
Send yourself a test
Compose a new email to yourself. Check that the signature appears, that any images load, and that the layout matches what you expect. Images are often blocked by default — see the section on image blocking below.
Adding Your Signature in Outlook for Mac
Outlook for Mac has a completely different rendering engine from its Windows counterpart. It uses WebKit — the same engine behind Safari — which means it handles modern CSS much better than Outlook for Windows. However, the steps to add your signature are different.
Go to Preferences
In the top Apple menu bar, click Outlook → Preferences → Signatures (or use Cmd+, to open Preferences, then click Signatures).
Add a new signature
Click the + button in the lower-left of the Signatures window. A new signature entry appears in the left column — give it a name.
Paste your content
Click into the editing area on the right side. Paste your formatted signature content. On Mac, Outlook renders this preview using WebKit, so what you see is closer to what most recipients will see.
Assign to your account
Close the Preferences window. Open a new email — in the compose window, click the Signature button in the toolbar to select or assign your signature. You can also set defaults per account in the Signatures preference panel using the "Account" dropdown.
Adding Your Signature in Outlook on the Web (OWA / outlook.com)
Outlook on the web — whether that's outlook.com, Office 365's web version, or an on-premises Exchange OWA deployment — has its own signature settings, separate from any desktop app. Signatures set in the desktop app do not sync to the web version automatically.
Open Settings
Click the ⚙️ gear icon in the top-right corner of Outlook web. At the bottom of the Quick Settings panel, click "View all Outlook settings."
Navigate to Email Signature
In the full settings panel, go to Mail → Compose and reply. You'll find the "Email signature" section here with a rich text editor.
Paste your signature
Paste your formatted signature into the editor. Outlook on the web uses a browser-based renderer, so it handles HTML significantly better than the desktop Windows version. Modern CSS is supported here.
Set defaults and save
Toggle "Automatically include my signature on new messages I compose" and "Automatically include my signature on messages I forward or reply to" as needed. Click Save.
Outlook Mobile (iOS and Android)
Outlook's mobile apps (iOS and Android) support signatures, but with significant limitations. Mobile Outlook signatures are plain text only — you cannot insert an HTML signature with images, tables, or styled text through the app's native settings.
To set a mobile signature:
- Open the Outlook mobile app → tap your profile picture → Settings → your account name → Signature
- Type a plain-text signature — name, title, phone number
- This signature appears on emails sent from the mobile app only
If you want an HTML signature to appear when sending from mobile, the only reliable approach is to use a third-party mail client on mobile (such as Gmail for iOS/Android) configured with your email account — or to draft emails in Outlook on the web from your mobile browser, where the full HTML signature is available.
Why HTML Signatures Look Different in Outlook
This deserves its own section because it causes enormous confusion. Here is what is actually happening:
Outlook 2007, 2010, 2013, 2016, 2019 (Windows) all use Microsoft Word's HTML rendering engine — specifically the same engine that renders Word documents. This engine was designed for documents, not web pages, and it has never been updated to support modern web standards.
What Word's renderer strips or ignores:
- Flexbox and CSS Grid — both completely ignored. Elements collapse or stack incorrectly.
- CSS background images — stripped from HTML email by default
- Border-radius — rounded corners do not render in Outlook 2007–2016 (partial support in 2019+)
- max-width on images — Outlook often ignores this, causing oversized images
- Line-height — inconsistently applied; different from browser rendering
- Percentage widths — often unreliable; fixed pixel widths work more predictably
- SVG images — not rendered at all; use PNG instead
- Web fonts — stripped; only system fonts render reliably
The consequence is that a signature designed with modern CSS will look correct in Gmail, Apple Mail, and Outlook for Mac — but will break in Outlook for Windows.
The solution is to design your signature using HTML tables and inline CSS only. Tables have been supported by Word's renderer since Outlook 2003. Every styling property should be applied inline (as style="" attributes on HTML elements), not in a <style> block, because Outlook strips stylesheet blocks in some versions.
Outlook-Specific Quirks You Need to Know
1. Images Are Blocked by Default
In Outlook for Windows, images in email are blocked by default as a security measure. Recipients see a broken image placeholder instead of your photo or logo. They must click "Download Pictures" or add your email address to their trusted senders to unblock images.
This is a known limitation and there is no way to force images to load. However, you can minimise the impact:
- Always add an
altattribute to every image so recipients see meaningful text even when images are blocked - Ensure your text-only signature still conveys all essential contact information without relying on images
- If your company uses Exchange, IT can configure automatic download of images from trusted domains
2. DPI Scaling on Windows
Windows DPI scaling (used on high-DPI displays running at 125%, 150%, or 200% scaling) causes Outlook to scale images differently than other applications. An image specified at 200px wide may render at 150px or 250px depending on the user's display scaling settings.
To handle this: always specify both the HTML width attribute and a corresponding inline CSS style="width:200px" on image tags. Using both gives Outlook two instructions to work from, which improves consistency.
3. Line Height Differences
Outlook renders line heights differently from browsers. A line-height: 1.5 set on a paragraph in a browser will display noticeably differently in Outlook for Windows. For signatures, it is safer to use fixed pixel values (e.g., line-height: 22px) rather than unitless multipliers, as pixel values are more consistently interpreted by Word's renderer.
4. Margin Collapse
CSS margin collapsing — where adjacent top and bottom margins merge into one — behaves differently in Outlook. Spacing between table rows or between paragraphs may appear larger or smaller than expected. Use table cell padding instead of paragraph margins to control spacing in Outlook-targeted signatures.
How to Make Your Outlook Signature Match Gmail
The goal for most people is a single signature design that looks consistent across Gmail and Outlook. Here is the formula that works:
Signature compatibility checklist
- Use an HTML table for layout (two columns: photo left, details right)
- All CSS properties applied inline — no <style> block
- Images hosted at a publicly accessible URL (not Google Drive or Dropbox)
- Images specified with both HTML width attribute and inline CSS width
- PNG format for images (not SVG)
- System-safe fonts: Arial, Verdana, Georgia, Times New Roman
- Fixed pixel widths, not percentages
- No flexbox, no CSS Grid, no CSS transitions
- Alt text on every image
- Tested in both Gmail and Outlook before rolling out
Building this manually is tedious. Every property has to be inlined, every table cell padded explicitly, every image double-specified. This is exactly why signature generators exist — they output Outlook-compatible table HTML so you don't have to hand-code it.
Frequently Asked Questions
Why does my signature look fine when I compose but wrong when the recipient receives it?
The compose view in Outlook uses one renderer; the email as sent and received may be processed differently depending on how your HTML is structured. Always test by sending to a Gmail account and opening in both Gmail and a separate Outlook instance. If it breaks on receipt but not in compose, the issue is typically CSS that Outlook strips from outgoing mail (it applies different rules to composing vs. rendering received mail).
My photo appears as a red X or broken image placeholder. What's wrong?
This is Outlook's image blocking. The recipient (or your own Outlook instance) is blocking externally loaded images by default. To test, right-click the broken image and select "Download Pictures." For a permanent fix, ensure your email address is in the recipient's trusted senders, or have your IT team configure automatic image loading for your domain. Also verify your image URL is publicly accessible in an incognito browser window.
Can I use the same signature in Outlook and Gmail?
Yes — but the signature must be designed with Outlook's rendering limitations in mind. Table-based HTML with inline CSS works in both. If you use a signature generator, make sure it explicitly outputs Outlook-compatible code. Our generator does this by default.
My signature appears twice — once from the template and once pasted manually. How do I fix this?
This happens when both an automatic default signature is set AND you manually insert a signature while composing. Go to File → Options → Mail → Signatures and check your "New messages" and "Replies/forwards" default settings. If you have a default assigned, do not also manually insert the signature when composing — it will appear twice.
Does Outlook support emoji in signatures?
Outlook for Windows has inconsistent emoji support. Basic emoji may render in Outlook 2019 and Microsoft 365, but older versions (2016 and earlier) often show blank boxes or question marks instead of emoji. If you need cross-version compatibility, avoid emoji in Outlook signatures.
How do I add a signature to a shared mailbox or alias in Outlook?
In Outlook for Windows, go to File → Options → Mail → Signatures. In the "Choose default signature" section, use the "E-mail account" dropdown to select your shared mailbox or alias, then assign a signature to it. You need to have the shared mailbox added as an account in Outlook (not just permissions access) for it to appear in this dropdown.
Why does my signature's font look different on the recipient's screen?
If you used a custom or Google Font in your signature, Outlook will not load it — it strips web fonts and falls back to the system default (usually Calibri or Times New Roman). Always design with system-safe fonts: Arial, Verdana, Georgia, or Tahoma. These render consistently without any external font loading.
Build an Outlook-compatible signature today
Send Like a Pro generates table-based HTML that works in Outlook 2016, 2019, 2021, Microsoft 365, and Gmail. No payment needed to preview — $8 to own forever.
Create Your Signature →Sources & further reading
- Microsoft — Add a signature to messages in Outlook: support.microsoft.com
- Email on Acid — Outlook rendering issues explained: emailonacid.com
- Litmus — Email rendering: why Outlook is different: litmus.com
- Microsoft Docs — High DPI display support in Office: docs.microsoft.com
