Deliverability describes whether your emails land in recipients’ inboxes. It is different from delivery rate, which only counts messages the receiving server accepted; an accepted message can still go to spam. Mailbox providers like Gmail, Yahoo and Outlook decide placement using authentication, the reputation of your domain and IP addresses, complaint rates and how recipients engage.
What mailbox providers look at
- Authentication: valid SPF and DKIM, and a DMARC policy aligned with your From domain.
- Domain and IP reputation built over time from sending behavior.
- Spam complaint rate: how often recipients mark you as spam.
- Bounces from invalid addresses, which suggest a poorly kept list.
- Engagement: opens, replies, moves out of spam, deletes without reading.
- Easy unsubscribing, including one-click unsubscribe headers for bulk mail.
Bulk sender requirements
Since February 2024, Gmail and Yahoo require bulk senders (Google defines this as close to 5,000 or more messages a day to personal Gmail accounts) to authenticate with SPF and DKIM, publish DMARC, support one-click unsubscribe and keep spam rates low. Google’s sender guidelines say to keep the user-reported spam rate below 0.1% and never reach 0.3%. Microsoft announced similar requirements for Outlook consumer domains in 2025.
Practical habits
Separate marketing and transactional mail, often on different subdomains, so a marketing problem does not block password resets. Warm up new domains and IPs gradually. Remove addresses that hard bounce and suppress people who have not engaged in a long time. Watch Google Postmaster Tools and your email platform’s reports.
Example
A sudden drop
Hypothetical company Cranmere sees clicks on its newsletter fall sharply. Postmaster Tools shows a rise in spam complaints after it emailed an old webinar list. It suppresses that segment, adds a clear unsubscribe link at the top of the next send, and watches reputation recover over the following weeks.
Common mistakes
Sending cold outreach from the main domain
Complaints from cold email can damage the reputation of the domain your customers rely on. Keep cold outreach separate, and within the law.
Questions
Not precisely. Seed-list tests and Postmaster Tools give indications, but providers do not report where each message landed.
