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12 email signature mistakes that hurt your brand (and how to fix them)

Logo as an attachment, image-only signature, missing fonts, outdated details… The most common email signature mistakes and the fix for each one.

The Soniako team Published 3 min read

An email signature is read thousands of times a year, yet almost nobody proofreads it. Here are the twelve mistakes we see most often, from the most visible to the most insidious — with the fix for each.

Formatting mistakes

1. The logo arrives as an attachment

Symptom: a paperclip on every email, and the recipient receives “image001.png”. It usually happens when the logo is pasted from a document instead of hosted online.

Fix: host images on an HTTPS server and reference them by URL. Full details in our image best practices.

2. The whole signature is one image

Tempting for a pixel-perfect look, but a false good idea: invisible when images are blocked, unreadable for screen readers, impossible to copy. Contact details must be text.

3. A font the recipient doesn’t have

The brand font installed on your laptop doesn’t exist on your customer’s. The email client swaps in a default — often Times New Roman in Outlook. Fix: use system fonts (Arial, Helvetica, Verdana, Georgia) with a fallback stack.

4. Blurry or distorted images

A 600-pixel logo squeezed to 150 by the email client, or a tiny logo stretched up, shows immediately. On high-density screens, a logo without a 2x version looks fuzzy.

5. A signature that’s too long

Fifteen lines, three banners, six social icons and a ten-line disclaimer: the signature ends up longer than the message. Aim for 4 to 7 lines of text. See the essential elements.

6. Unreadable in dark mode

Black logo on a transparent background, forced dark-grey text: in dark mode half the signature vanishes. The topic deserves its own article.

Content mistakes

7. Outdated information

Old job title, old number, old office address, old logo. It is the most frequent mistake and the most costly for credibility. It always has the same cause: each signature is maintained by hand. Fix: feed the signature from the company directory through automatic sync.

Landline, mobile, switchboard, fax, three social networks, two websites: too much choice kills action. Keep the channel you actually want people to use.

A link to a deleted page, a LinkedIn profile whose URL changed, a campaign that ended months ago. Every link in a signature needs an owner and a review date.

10. Missing mandatory details

Depending on your country, some company details may be required in business correspondence. They are often missing from home-made signatures. See email signature legal requirements.

Organizational mistakes

11. Everyone has their own version

When ten people have ten different signatures, the recipient doesn’t see a brand — they see ten people improvising. Inconsistency is the most widespread problem, and the least visible from inside the company.

12. A forgotten banner

A “Trade show 2025” banner still showing in 2026 is worse than no banner at all. Every banner needs a start date and an end date. That is the point of scheduling campaigns.

The common cause: manual management

Reading back through this list, most of these mistakes share one origin: the signature is copied, pasted and maintained by hand, by each person. Training everyone isn’t enough, because data changes and new people join.

The lasting fix is to centralize signature management: one approved template, data from the directory, automatic deployment, and visibility on who has the right version.

Quick checklist

Before signing off on a signature, check that:

  • Text stays readable with images blocked
  • No image arrives as an attachment
  • It renders correctly in Outlook, Gmail and on mobile
  • The logo is sharp on high-density screens
  • The signature is readable in dark mode
  • Every link works
  • Mandatory details are present
  • The banner has an end date

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