An email signature that stays out of spam

An email signature rarely sends a message to spam on its own. The trouble usually comes from four places: images attached instead of hosted, bloated code, links that hide where they go and, most often, a domain without SPF, DKIM and DMARC. Fix them one by one and the signature stops being a problem.

We went through this with our own signature: it's HTML, it has an animated logo (a GIF) hosted on our site rather than attached, and the first frame of the animation is complete. Here's why each of those choices matters.

Start with the domain: SPF, DKIM and DMARC

Before any design work, check that the domain you send from is authenticated. Without it, even the nicest signature lands in spam.

What each one does, briefly:

• SPF is a list, published in DNS, of the servers allowed to send mail for your domain.
• DKIM adds a digital signature to each message, so the receiver can check it wasn't altered on the way.
• DMARC tells the receiving server what to do with messages that fail those checks, and sends you reports.

Since 2024, the big mailbox providers have tightened the rules. Starting February 1, 2024, Google requires anyone sending to Gmail accounts to have at least SPF or DKIM and to keep the reported spam rate below 0.3%. Anyone sending more than 5,000 messages a day also needs DMARC and one-click unsubscribe on marketing mail. Yahoo announced nearly identical rules, also enforced from February 2024. Microsoft followed: since May 5, 2025, domains sending more than 5,000 messages a day to Outlook.com, Hotmail and Live addresses must pass SPF and DKIM and publish DMARC with at least p=none, or their mail goes to Junk.

A small business rarely sends 5,000 emails a day, but set up all three anyway. You do it once, with your email provider and in DNS, and the DMARC reports show you whether someone is sending fake mail in your name.

Host the image, don't attach it

The logo in a signature can reach the recipient in two ways. Attached (or embedded in the message), the file travels with every email: it adds size, shows up for some recipients as an attachment with a paperclip and, if it's pasted straight into the code as base64, bloats the HTML. Hosted on your site, the email only carries a link to the image, and the mail app loads it from there.

We use the hosted option, on our own domain, over https. Two practical details:

1. give the image alt text with your company name, so there's still something to read when images are blocked;
2. set a fixed width and height in the code, so the signature doesn't blow up across the screen on a phone.

Animated GIFs and the first frame

An animated logo catches the eye, but not every email client plays it. Outlook for Windows, versions 2007 through 2019, doesn't play animated GIFs and shows a single frame. The advice from email guides is simple: the first frame has to contain everything important, so it works as a static image too.

That's why the first frame of our signature is the full logo, not a blank screen the logo animates out of. Anyone opening the email in Outlook sees a normal signature; everyone else sees the animation. Keep the GIF small: a few frames, few colors, a reasonable file size.

Message weight: the 102 KB line

Gmail clips messages whose HTML goes past roughly 102 KB. The recipient sees a notice that the message was clipped and a link to the rest, and whatever sits below, often the signature itself, disappears. Google's sender guidelines don't give the number; it's documented by email marketing providers, who run into it every day.

A normal signature won't reach 102 KB by itself. But one copied from Word or an online generator can drag along a lot of hidden code, and in a long reply thread, where the signature repeats under every message, the total adds up fast. To check: in Gmail, open the sent message, choose "Show original" and look at the size, or download the message as an .eml file.

Real text and links you can see

Google's sender guidelines say links in the message should be visible and easy to understand, HTML should follow the standards, and you shouldn't use HTML and CSS to hide content. That gives you three rules for a signature:

• Name, title and phone as text, not one image with everything in it. An image-only signature can't be copied, can't be read when images are blocked, and looks a lot like spam.
• No link shorteners. A shortened link hides where it goes. Use your real address, on your own domain.
• Few links. Your website, maybe a contact page or a digital business card. Five social icons don't help anyone.

Dark mode and phones

Many mail apps invert colors in dark mode. A black logo on a transparent background vanishes on a black screen. The fix: put the logo on its own background, white or colored, or use a version with a light outline.

On a phone, the signature has to fit the screen width. Large fixed widths, left over from signatures built on a desktop, push everything to the right and force sideways scrolling. Test on an iPhone, on Android in the Gmail app, and in Outlook on a desktop before you roll it out to the whole team.

Checklist

If you want a signature that's built and tested across email clients, we make it along with the rest of your communication materials. See our marketing services.