What is email deliverability?

These are two different things. A message can be accepted by the receiving server and still land in spam. "Delivered" says the server took it. Inbox placement, the heart of deliverability, asks where it ended up.

So a dashboard that says "delivered" does not tell you how many people could see the email. Ask which one it measures.

Google's sender guidelines name the main things. In plain terms:

• Prove the mail is yours. That is sender authentication. Gmail asks every sender for SPF or DKIM, and senders of more than 5,000 messages a day to Gmail accounts for SPF, DKIM and DMARC¹. DMARC tells receiving servers what to do with messages that fail authentication.
• Make leaving easy. Those larger senders must support one-click unsubscribe on marketing and subscribed messages¹.
• Keep complaints low. The spam complaint rate is the share of inbox-delivered messages that people mark as spam. Gmail asks all senders to keep it below 0.3% in Postmaster Tools¹. Yahoo also sets 0.3%².
• Send steadily. Google's list of common sender issues warns that raising volume too quickly can cause delivery issues³.

Google's Postmaster Tools shows how your domain is doing for Gmail recipients, including spam rate and compliance status⁴. That is the place to look first.

The full list of provider rules is in Gmail Yahoo bulk sender requirements. For the wider programme, see customer retention strategy ecommerce.

For ZFD: Our view is that someone should own the Postmaster Tools check by name. If everyone owns it, nobody looks.

Not necessarily. A drop in open rate can mean fewer people saw your email. It can also mean the way opens are counted changed. Apple Mail Privacy Protection downloads email content in the background, so senders cannot see whether a message was opened. Check complaints and inbox placement before you blame the subject line.