An email signature banner is a wide promotional image under your contact details. The safest version is short, hosted somewhere you control, backed by a text link, and given an end date. The one hard size figure from a vendor comes from Google: an image in an admin-set footer should be 70 to 100 pixels high and 300 to 400 wide, with a maximum of 100 high and 1000 wide.
Those figures come from Google’s page on Workspace signatures, last updated on 1 October 2026. We also read Microsoft’s pages on picture downloads, organization-wide signatures and accessible Outlook email, all in October 2026. We found no vendor size limit for a banner in a personal signature, so the other numbers here are our own rules of thumb and are labelled.
Email signature banner: six rules
- Size: stay within 100 pixels high, the ceiling Google gives for an admin footer.
- Weight: keep the file small (our rule: under 50 KB).
- Host: decide where the file lives before you design it.
- Alt text: put the words and the action in the alt text, not “banner”.
- Link: add a text link as well, since pictures are often blocked.
- End date: write the removal date into the brief on day one.
Banner size for an email signature banner
Google’s numbers describe the image that goes into the footer. A 400 by 100 banner shown at that size is inside the recommended range. If you export it at double size for sharp screens, as we suggest for logos in our size guide, the file becomes 800 by 200, which is over Google’s stated maximum height for footers.
So pick one. For an admin-set footer, stay inside Google’s limit. For a personal signature, where Google gives no pixel limit, we suggest 600 pixels as the widest you display, because emailfooter’s own signatures are 600 pixels wide, and 100 pixels as the tallest, so the banner never outweighs the contact details. Both are our rule of thumb, not a vendor figure.
Gmail adds a cap of its own. A signature may hold 10,000 characters, and Google’s help page counts any image against that allowance, suggesting a resize if saving fails.
Where to host an email signature banner
The file has to live somewhere, and each choice has a catch that the vendors state.
| Option | What the vendor page says | Catch |
|---|---|---|
| Upload in Gmail | Settings, General, Signature, Insert image, then Upload | Counts toward the 10,000 characters |
| Google Drive | Insert image, then My Drive | Must be shared publicly for the image to appear |
| Web address | Insert image, then Web Address (URL) | The file must stay online at that address |
| Admin footer in Google Workspace | Admin console, Compliance, Append footer | The 70 to 100 by 300 to 400 pixel guidance above |
| Microsoft 365 organization-wide rule | Exchange admin center, Mail flow, Rules | The page lists “You can’t embed images in email signatures” as a limitation |
| Classic Outlook | The Image button in the signature editor | Microsoft warns that VML tags can make elements appear as attachments |
A web address on your own site has one benefit that we think is real but have not tested: if every signature points to the same file, replacing the file changes the banner for everyone who still shows it. Email apps may keep their own copy for a while, so do not expect it to be instant.
These steps follow Google’s help page, read in October 2026. Our guide to adding an image to a Gmail signature goes through them in more detail.
What the reader may see instead
On a fresh install, Microsoft says, classic Outlook does not fetch pictures from the internet by itself. It lists four reasons, one of them tracking pixels. In place of the picture the reader gets an information bar at the top of the message, with a Download Pictures choice for that message.
For a banner, that means many readers will see a gap or the alt text. Treat the banner as a bonus, never as the only copy of anything. Microsoft’s accessibility page says it directly: if you must use an image that contains text, repeat that text in the message.
An alt text pattern for an email signature banner
Microsoft asks for alt text that conveys the content and purpose of the image in a concise, unambiguous way, no longer than a short sentence or two, and without phrases such as “an image of”. Our pattern for a banner is: what it is, when, and what to do.
- Event: “Open day on 14 November. Book a place at harbourstudio.example/open-day”
- Award: “Winner of the 2026 Regional Design Award”
- Newsletter: “Monthly design notes. Subscribe at harbourstudio.example/notes”
Do not write “banner” or “graphic” in any of them. Then add a plain text link on the line above the banner, so the offer still works when the picture does not load. Our guide to adding a link to an email signature covers the markup.
Types of email signature banner and their clutter risk
This table is our judgement. We have no survey or test behind it.
| Banner type | Clutter risk | Retire when |
|---|---|---|
| Event or webinar | High | The day after the event |
| Seasonal offer | High | The offer ends |
| Product launch | Medium | Four to six weeks after launch |
| Award or accreditation badge | Low | The award is superseded, or after one year |
| Newsletter sign-up | Medium | You have not changed it in a quarter |
| Regulatory logo | Low | Never, if you must show it |
A banner turns every reply in a long thread into an advert, so we allow one at a time and none for people who mostly write to existing clients.
When to retire an email signature banner
The rule is simple. Write the end date on the request before the banner is made, and put a calendar reminder on the date. Remove the banner within a week, whether or not anyone has noticed it. A banner with no end date is the usual way a signature goes stale.
Counting results needs its own tool, because emailfooter has no click analytics. It records copies and installs, not link clicks. Our articles on email signature analytics and signature marketing campaigns look at what you can measure.
What emailfooter can and cannot do with a banner
emailfooter has no banner field. The closest it gets is the logo, which the admin can place above, below, left or right of the details, at a width of 40 to 260 pixels. A wide logo below the details behaves like a banner, and it is set once for the whole company.
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The nearest emailfooter gets to a banner: a wide logo placed below the details. The wording is a stand-in. The company and person are made up.
If your campaign needs a separate promotional image for each department, set it up in your mail app’s own signature editor, or use a tool built for that. Staff install the signature themselves, so a changed logo means each person repeating the install step.
Frequently asked questions
What size should an email signature banner be?
Google recommends 70 to 100 pixels high by 300 to 400 wide for an image in an admin-set footer, with a maximum of 100 by 1000. For personal signatures we found no limit, so 600 by 100 is our own rule of thumb.
Should I put an email signature banner in my email signature?
Only if there is something to promote and a date to remove it. Otherwise it adds height and clutter. Keep the contact details as text.
How do I add a banner in a Gmail signature?
Go to Settings > See all settings, find Signature, click Insert image, and choose Upload, My Drive or Web Address (URL). Images from Drive must be shared publicly to appear.
Does an email signature banner count toward Gmail’s character limit?
Yes. Google counts the image against the 10,000 character allowance, and a resize is its suggested fix when saving fails.
Why does my banner in an email signature not show?
Classic Outlook may be holding the picture back, and the reader sees a bar offering Download Pictures. Add alt text and a text link.
Keep reading
- Email signature analytics: how to measure clicks without a paid tool: Email signature analytics without a paid tool: tag signature links with UTM parameters, read the clicks in Google Analytics, and know what you cannot measure.
- Email signature marketing campaign: a banner plan for your whole team: Plan an email signature marketing campaign in seven steps: goal, banner, tagged link, dates and retirement, with honest expectations on volume and cost.
- Email signature size: width, image size and character limits: What is the best email signature size? Recommended width, logo dimensions, image file weight and the character limits in Gmail, so your signature looks right.
- Email signature design: layout, spacing, colour and hierarchy rules: Email signature design as a one-page spec: width, grid, type scale, spacing and colour count, plus two before-and-after redesigns and a contrast check.
Make every signature in your company match
emailfooter is a free WordPress plugin. You design the signature once, and each person adds their own details and installs it in their mail app. Prefer not to run a website? emailfooter Managed is the same software, hosted for you.