Does AI-written cold email hurt deliverability or damage your domain?

Is there evidence that Gmail penalises AI-written email?

Not in anything we could open from Google, Yahoo or Microsoft. Google's sender FAQ covers authentication, spam rate and unsubscribe handling, and says nothing about AI-written content². Its help page on why Gmail marks a message as spam lists spoofed addresses, phishing, unconfirmed senders, administrator rules, senders you unsubscribed from, empty messages and senders you reported before⁵. AI authorship is not on the list.

Claims that Gmail detects AI text, or that give exact spam-flag percentages for AI email, are common on vendor blogs. We found no study or Google statement behind them, so this page does not repeat their numbers. Absence of evidence is not proof, because mailbox providers do not publish their filters. What we can say is that every published requirement is about behaviour you control.

What actually sends cold email to spam?

The documented triggers, with the source for each:

• Spam complaints. Google says to keep the rate below 0.10 percent and never let it reach 0.30 percent. Bulk senders above 0.3 percent became ineligible for mitigation from June 2024 until they stay below it for 7 consecutive days².
• Weak authentication. Unauthenticated mail can be marked as spam or rejected with a 5.7.26 error¹.
• Sudden volume. Google advises increasing volume gradually and avoiding spikes, and says to cut volume when mail bounces or is deferred until the errors drop¹.
• Hard-to-use unsubscribe. Yahoo says to honour unsubscribes within 2 days³, and Google requires one-click unsubscribe above the bulk threshold¹.
• Misleading sender details. Google says display names must identify the sender, must not deceive, and must not impersonate others¹.

Where does AI make deliverability worse?

AI changes the cost of sending, not the rules. It lets one person produce thousands of near-identical messages and add mailboxes, which raises volume faster than reputation can follow. Complaints rise when recipients feel a message was not meant for them, and that is a risk of how AI is used, not a filter on AI text.

Warm-up advice from sellers is cautious. Instantly, which sells sending software, advises 20 to 50 emails a day from a new inbox and up to 100 a day from a seasoned inbox after a 4 to 6 week warm-up⁶. Treat those as one vendor's operating habits, not a Google limit.

How do you know if your domain is already damaged?

Google Postmaster Tools reports how often recipients mark your mail as spam, why messages may not be delivered, whether messages are authenticated, and your domain or IP reputation¹. That is the first place to look, before changing anything.

Error codes are the second. A 5.7.26 rejection points to authentication, while a 4.7.28 deferral means you exceeded a quota. Google advises waiting at least 10 minutes, then sending from a single connection and adding connections one at a time, and cutting volume when mail bounces or is deferred until the error rate drops, then raising it slowly¹. Google also warns that senders who ignore its best practices may not be considered for deliverability mitigations¹.

What should you set up before the first send?

• SPF, DKIM and a DMARC policy on the sending domain, even if you send far fewer than 5,000 a day. Outlook's own FAQ says all senders benefit from these practices⁴.
• A working unsubscribe that you honour within 2 days³.
• Google Postmaster Tools, so you can watch your spam rate against the 0.3 percent line¹.
• Small, gradual sends to a verified list, and a person who reads replies and complaints.
• A lawful ground for each recipient, covered in is cold email legal in India.