Guide · Deliverability

Email deliverability: SPF, DKIM, DMARC and Gmail's rules

The short answer

To land in the inbox, authenticate your domain (SPF, DKIM and, for bulk senders, DMARC), keep spam complaints low, and make unsubscribing easy. Gmail spells these out in its sender guidelines, and they apply to cold email too.^[1]

Updated 6 Oct 2026 Facts link to their sources

SPF, DKIM and DMARC in one minute

SPF is a DNS record listing the servers allowed to send email for your domain.
DKIM signs each email with a key published in your DNS, so receivers can check it wasn't forged or changed.
DMARC tells receivers what to do when SPF or DKIM fail, and where to send reports.

Gmail sets a minimum DKIM key length of 1024 bits and recommends 2048.^[1]

Gmail's rules for all senders

From Gmail's email sender guidelines:^[1]

Set up SPF or DKIM for your sending domain.
Have valid forward and reverse DNS (PTR) records for your sending IPs.
Use a TLS connection to send.
Keep the spam rate reported in Postmaster Tools below 0.3%.
Format messages to the RFC 5322 standard, and don't impersonate Gmail From: headers.

Extra rules for bulk senders

If you send 5,000 or more messages a day to Gmail accounts, Gmail also requires:^[1]

Both SPF and DKIM, plus DMARC for your sending domain.
A From: domain aligned with your SPF or DKIM domain.
One-click unsubscribe for marketing and subscribed messages, with a clearly visible unsubscribe link in the body.

Warming up a mailbox

A new mailbox or domain has no sending history, so start small. Send a handful of emails a day, mostly to people likely to reply, and increase volume gradually over a few weeks while you watch replies and bounces. If complaints rise, slow down. Keep cold volume per mailbox well under Gmail's caps: see Gmail sending limits.

Unsubscribes

In the US, CAN-SPAM requires a clear way to opt out of commercial email and that you honor opt-outs within 10 business days.^[2] Make it one click, and stop every sequence for that person.

Meerko adds a visible unsubscribe link and one-click unsubscribe headers to every sequence email, and an unsubscribe stops every sequence in your workspace for that address. What you send still matters most: short, relevant emails and a few well-spaced follow-ups.

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FAQ

Do I need SPF, DKIM and DMARC for cold email?

Gmail requires SPF or DKIM from every sender, and SPF, DKIM and DMARC from anyone sending 5,000 or more messages a day to Gmail. Setting up all three is the safe default.

What spam rate does Gmail allow?

Gmail's sender guidelines ask senders to keep the spam rate reported in Postmaster Tools below 0.3%.

Do cold emails need an unsubscribe link?

In the US, CAN-SPAM requires a clear way to opt out of commercial email, honored within 10 business days. Gmail also requires one-click unsubscribe for marketing messages from bulk senders.