Teams that come from newsletters bring newsletter habits into cold email: a logo in the signature, a styled button, an unsubscribe footer. Each looks like a detail. To a filter reading mail from an unknown sender, each is evidence. Below: why filters treat formatting as a phishing signal, what a signature link and footer cost in a measured test, what a cold-email signature should contain, and when one link is fine.
What is a plain text email?
A plain text email contains only characters. The mail client shows it in the reader's default font, with no layout, and any URL appears as written. Most marketing email is HTML instead: a small web page with images, tables, styled text and a hidden image that reports when the message is opened.
A cold email should look like mail one person types to another. Plain text, or HTML so minimal that it renders like plain text, is what that mail looks like, to the filter and to the recipient.
Why do filters treat formatting as a phishing signal?
Because cold email and phishing look almost the same to a machine. Both are unexpected, both come from someone the recipient has no history with, and both ask the recipient to do something. A filter separates them with the signals it can read, and the strongest are the ones a marketer is tempted to add.
- Images: heavily flagged and loaded from a remote server. The tracking pixel is an image too.
- Links: especially tracked or redirected links, or several links in a short message. Spamhaus notes that receiving systems have to examine links because of phishing.
- Heavy formatting: HTML layout, styled buttons, coloured text and tables.
- Bulk markers: an unsubscribe footer tells the filter the message went to a list, not to a person.
Once a filter flags a domain for these signals, deliverability for that domain drops sharply and does not recover quickly.
HubSpot's plain text versus HTML data shows simpler emails winning every A/B test it ran and a GIF cutting clicks by 42%, in a newsletter context. Spamhaus explains that receiving systems examine links because of phishing, which is why every link carries a cost. Google's sender guidelines make one-click unsubscribe mandatory for bulk senders above 5,000 messages a day; one-to-one cold email below that threshold is a different regime, though laws such as CAN-SPAM still require an opt-out.
What did a signature link and a footer cost in reply rate?
Several percentage points. In Leadspicker's own test, a link to the company website in the signature and an unsubscribe link in the footer lowered reply rate by several percentage points. Moving the same content to plain text brought it back.
- Change tested: website link in the signature plus unsubscribe link in the footer, against the same message in plain text.
- Metric: reply rate, not opens or clicks.
- Result: several percentage points lower with the link and footer; recovered in plain text.
- Not yet published: sample size, period and the exact difference.
External data points the same way in a different setting. HubSpot's A/B tests on its own marketing emails found that the simpler version won every test it ran, at least 13, and that a GIF cut clicks by 42%. Those were newsletters to subscribers, not cold email, so read them as direction rather than a benchmark.
What should a cold-email signature contain?
Name, role and company, and nothing that needs to load.
| Designed signature | Plain text signature | |
|---|---|---|
| Name and role | Styled and coloured, inside a table | Typed on one line |
| Company | Logo image | Company name as text |
| Links | Website, social icons, booking button | None, or one where it helps |
| Footer | Unsubscribe link and legal block | A plain sentence inviting a no |
| What the filter sees | Images, several links, layout, bulk footer | Text from a person |
Leadspicker's formatting rules for cold email:
- Write as if typing to one person in your own mail client.
- Use a text signature: name, role, company.
- No logo, no banner, no image at all.
- One link at most, and only where it helps the reader.
- Leave open tracking off, because the pixel is an image.
The footer needs care, not removal of the opt-out. Google requires one-click unsubscribe from senders of more than 5,000 messages a day to Gmail; one-to-one cold email at a few messages per mailbox per day sits far below that threshold. That is not a legal verdict. In the US, CAN-SPAM requires an opt-out in commercial email at any volume, and other countries have their own rules, so keep a way to say no even without a footer link.
When is one link acceptable?
When the reader needs it to act and nothing else in the message is a link. A link to a page that answers the question your email raises can earn its place. A website link in the signature does not: the recipient can find the company by its name.
Keep that one link bare and untracked. A redirected tracking link adds a domain the filter must check, and security gateways open links in a sandbox before anyone reads the message, which also makes click data unreliable.
In a Leadspicker experiment, a website link in the signature and an unsubscribe link in the footer lowered reply rate by several percentage points; plain text brought it back.
Frequently asked questions
Is plain text better than HTML for cold email?
Yes. Images, links and styling are the signals filters use to separate phishing from real mail, and a cold email from an unknown sender is already under suspicion. Plain text looks like a message from a person.
Should a cold email include an unsubscribe link?
Google's one-click unsubscribe rule applies to bulk senders above 5,000 messages a day. Below that, a plain sentence inviting the recipient to say no keeps an opt-out without a footer link; check the law in each country you write to.
Can a cold email contain a link?
One, if the reader needs it to act and it is not tracked or redirected. Leave the website out of the signature and keep the first message link-free if you can.
