What is email deliverability and how do you protect your sender reputation?
Why good email lands in spam, and how to warm a new IP or sending domain safely.
Deliverability is whether your email reaches the inbox, not whether it was accepted. It is driven by a reputation mailbox providers keep on your sending domain and IP, based on complaints, bounces, engagement and consistency. Content matters far less than most people think.
The published thresholds
You do not have to guess at the numbers, because two of the largest mailbox providers publish them. Google's email sender guidelines tell senders to keep the spam rate reported in Postmaster Tools below 0.10 percent and to avoid ever reaching 0.30 percent. Yahoo's sender best practices state the same rule: keep your spam rate below 0.3 percent. Both also require valid forward and reverse DNS, meaning a PTR record that resolves, and Google requires a TLS connection for transmission.
Both providers also require authentication. Google requires SPF or DKIM for all senders, and SPF, DKIM and DMARC for anyone sending more than 5,000 messages per day to Gmail accounts. Yahoo requires SPF or DKIM at minimum and both plus a valid DMARC policy for bulk senders. Sign up for Google Postmaster Tools and Yahoo's Complaint Feedback Loop on day one. You cannot manage a number you cannot see.
Warming a new domain or IP
A brand new sending identity has no reputation, and a sudden large send from an unknown source looks exactly like a spam run. Google's own guidance is to start with a low sending volume to engaged users and increase slowly, to send at a consistent rate rather than in bursts, and to avoid sudden volume spikes, giving the example that immediately doubling previous volume can cause rate limiting or reputation drops. Google also says that if messages start bouncing or being deferred, reduce volume until the error rate falls, then increase slowly again.
In practice that means: start with the contacts most likely to open, send on a regular schedule, watch Postmaster Tools daily, and hold at the current volume any time the spam rate or deferral rate moves. Our practical walkthrough is in how to warm up a new IP address.
If the reputation is already damaged
Stop mailing the non-engaged immediately, suppress everyone who has not clicked in months, fix authentication, and rebuild volume slowly on the engaged core. Moving to a brand new domain without fixing the behavior just burns a second domain. Ongoing help is available on a service retainer.
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