The 16 rules that put a cold email in spam
These are the checks Quotarider runs on every message before it sends. Not a general list — the actual sixteen, in the order the engine applies them, with what each one is looking for.
Why a checklist beats a spam score
Spam scores are produced by a model on the receiving end that nobody outside that provider can see. Rules are different: they are things you either did or did not do, and you can fix them before you send. Every rule below is deterministic — the same email produces the same findings, with no model involved and nothing sent to one.
What the body is made of
Image-only. An email that is one image with no text is the oldest way to hide words a filter can read, and filters have known that for twenty years. If the text-to-image ratio collapses, this fires.
No plain-text fallback. A multipart message without a text part looks like it was generated by a tool that only cares about the HTML. Real mail clients send both.
Too short, or too long. Under about thirty words there is nothing for a filter to judge except the links. Over roughly two hundred and fifty, reply rates fall regardless of what the filter thinks.
What the links say about you
Link-heavy. The ratio of link text to body text. A first cold email with four links reads as a newsletter that was not asked for.
Many links. A count, separate from the ratio, because six links in a long email is still six links.
A shortener. bit.ly and its relatives are used to hide a destination, so filters treat them as hiding a destination. There is no upside in a sales email — you own the domain, use it.
A raw IP address. A link pointing at http://203.0.113.4/offer
is a link nobody legitimate sends. This is scored heavily and rightly.
What the subject line does
Length. Past roughly sixty characters the end is cut off on a phone, which is where most first opens happen.
SHOUTING. Capital letters across a whole subject.
Emoji in the subject. Filters do not ban them; recipients discount them. In a first cold email to somebody who has never heard of you, an emoji is a cost with no return.
Trigger words. A small list — "guarantee", "congratulations", "free money" and their neighbours. Not because a filter has a banned-word list in 2026, but because messages containing them are reported more often, and reports are what filters actually learn from.
What you owe the person receiving it
No unsubscribe. This is the one that has changed from advisable to
mandatory. Since 2024 Gmail and Yahoo require one-click unsubscribe — the
List-Unsubscribe-Post header, RFC 8058 — on bulk mail, and failing
messages are rejected rather than filtered. Rejected means it never arrives and
you are told nothing useful.
A generic greeting. "Dear Sir/Madam" or "Hi there" tells the reader they are one of a list. This is not a filter rule. It is in the checker because the reply rate difference is larger than any of the technical rules above.
The rule that matters more than these sixteen
Volume. Google counts bulk-sender volume per domain, not per mailbox — 5,000 messages in twenty-four hours across every address on that domain. Cross it and the technical rules above stop being advice and become enforcement, with rejection as the penalty. Most senders who get filtered were not writing bad emails; they were sending correct emails from a domain that had quietly crossed a line nobody was counting.
How the 5,000 line is counted →
Quotarider keeps the touch, the reply, the deal and the paid invoice in one database, behind a deliverability guardrail. Free plan, no card.