Email deliverability is the probability that an email you send lands in the recipient's inbox rather than the spam folder, promotions tab, or being rejected at the gateway. Deliverability is governed by sender reputation (built from your domain, IP, and historical engagement), authentication (SPF, DKIM, DMARC), and content signals. Healthy outbound senders maintain inbox placement above 90%; placement below 70% is a deliverability emergency.
What makes deliverability go bad?
Deliverability decays from a combination of signals, not a single cause. The largest factor is engagement: if recipients delete your emails without opening, report them as spam, or never reply, mailbox providers (Gmail, Outlook, Yahoo) learn your mail is unwanted and start filtering it. The second factor is technical setup: missing or misconfigured SPF, DKIM, or DMARC records make your mail look unauthenticated. The third is volume velocity: ramping a new sender domain from zero to 500 emails per day in a week looks identical to a spammer's pattern, which is why domain warmup is non-negotiable for new senders.
The fourth and most underrated factor is list hygiene. Sending to bounced or invalid addresses signals you scraped a bad list. A 5%+ bounce rate will tank reputation within 72 hours. Most deliverability problems in outbound trace back to skipping email verification before send.
How do you fix and protect deliverability?
Six practices, in order of impact. First, authenticate properly: SPF, DKIM, and DMARC set up correctly on every sender domain. Second, use a separate sender domain from your primary corporate domain (e.g., reachout-yourcompany.com instead of yourcompany.com) so a deliverability issue does not blow up your internal mail. Third, warm new domains for 4-8 weeks before scaling volume. Fourth, verify every email before sending; aim for under 2% hard bounce rate. Fifth, monitor reply rate as a leading indicator: when reply rate drops below 1%, deliverability is about to follow. Sixth, rotate sender mailboxes and pool sends across multiple addresses to spread reputation risk. ReachIQ Email Health automates this across Gmail, Outlook, and Yahoo.
Related questions
What is a "good" inbox placement rate?
Above 90% to the inbox (not promotions, not spam) is considered healthy for outbound B2B. Below 85% suggests reputation issues. Below 70% means your sender domain is being filtered as bulk or spam and needs immediate intervention, typically a warmup reset and content audit.
Can you test deliverability?
Yes. Tools like Mailtrap, GlockApps, MailReach, and Folderly run seed-list tests across major providers and report whether your mail lands in Gmail inbox, Outlook inbox, Yahoo inbox, and so on. Run a deliverability test before launching a new campaign and once a week during steady state.
Does sending volume affect deliverability?
Yes. Mailbox providers track velocity. Sending 50 emails per day for a month then jumping to 500 looks like compromise or a list buy. Ramp by 10-20% per week, and never exceed 50 sends per day per mailbox without dedicated pool management.