What is the difference between delivery rate and deliverability?

Delivery rate is the share of emails the receiving server accepted rather than bounced. Deliverability, or inbox placement, is whether accepted emails land in the inbox. A message can be delivered straight to spam.

What spam complaint rate do Gmail and Yahoo allow?

Both say to keep the spam rate below 0.3%. Google recommends staying below 0.1%, and since June 2024 bulk senders above 0.3% are ineligible for mitigation until they stay below it for seven consecutive days.

How do I check my deliverability?

Use Google Postmaster Tools for Gmail spam rate and domain reputation, check that SPF, DKIM and DMARC pass in a received message's headers, and watch bounce and reply rates by campaign.

Email deliverability: what it means

The three layers

Accepted or bounced. The receiving server either takes the message or refuses it. Refusals show up in your bounce rate.
Inbox or spam. Accepted mail is sorted by filters. You cannot see this directly, which makes it the hard part.
Read or ignored. Engagement feeds back into reputation. Mail people open, reply to and move out of spam helps; mail they delete unread or report hurts.

What Gmail and Yahoo require

From February 2024, Gmail and Yahoo began enforcing sender requirements. In summary, from their published guidelines:

Requirement	All senders	Bulk senders
Authentication	SPF or DKIM	SPF and DKIM, plus DMARC (policy can be p=none)
Alignment	Not required	From: domain aligned with the SPF or DKIM domain
Spam rate	Below 0.3%	Below 0.3%
Unsubscribe	Not required	One-click unsubscribe for marketing and subscribed mail
Other	Valid forward and reverse DNS (Gmail), TLS (Gmail), RFC 5322 format	Same

Google defines a bulk sender as one that sends close to 5,000 or more messages to personal Gmail accounts in 24 hours, counted across the primary domain, and that status is permanent once assigned. Yahoo asks bulk senders to honour unsubscribes within 2 days. Details are in SPF, DKIM and DMARC.

Worked example: what 0.3% means

Say you send 2,000 cold emails a week from one domain. 0.3% of 2,000 is 6. Six recipients pressing "report spam" in a week puts you at the limit. Google recommends staying under 0.1%, which is 2 complaints. Cold email has little margin, which is why targeting matters more than copy: people who clearly fit and have the problem rarely report a short, relevant note.

A deliverability checklist

Authenticate the sending domain with SPF, DKIM and DMARC.
Consider sending cold email from a separate domain from your main one, so problems stay contained.
Verify every address before sending (email verification).
Ramp volume gradually on new domains and inboxes.
Keep first emails plain: no images, few or no links, no attachments.
Stop sequences on replies, bounces and opt-outs, and keep a do-not-contact list.
Watch spam rate in Google Postmaster Tools.

Common mistakes

Buying volume over fit. More sends to weaker matches raises complaints.
Ignoring bounces. They signal a scraped list to filters.
Judging by open rate. Privacy features load images automatically, so opens do not show inbox placement.

How Sluice affects deliverability

Sluice sends only through your own connected Gmail or Outlook accounts, so your domain's authentication and reputation apply, and only messages you approve. Every address is verified before it is billed, and sequences stop on a reply, a "no", a bounce or the do-not-contact list. Sluice does not include inbox warmup; a dedicated sender such as Instantly is stronger there (Sluice vs Instantly).