Email deliverability is the ability of an email to successfully reach the recipient's inbox rather than being filtered into spam, promotions, or junk folders, or being rejected outright by the receiving mail server. For B2B cold email and marketing teams, deliverability is a foundational issue: a campaign with a 30 percent open rate is wasted if only half the emails actually reach the inbox.
Deliverability vs delivery rate
Delivery rate and deliverability are different metrics. Delivery rate measures whether an email was accepted by the receiving mail server (i.e., it was not bounced). An email can be delivered (accepted by the server) but still end up in spam. Deliverability is specifically about inbox placement: did the email reach the inbox where the recipient is likely to see it? Inbox placement rate is the more meaningful metric, but it requires a tool like GlockApps, Litmus, or 250ok to measure accurately.
Key factors that affect email deliverability
- Sender reputation: internet service providers (ISPs) and email providers assign a reputation score to sending domains and IP addresses based on historical sending behavior. High bounce rates, spam complaints, and sending to purchased lists all damage reputation. Reputation is the single biggest determinant of inbox placement.
- Authentication: email authentication protocols prove to receiving servers that you are who you say you are. The three main standards are SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance). All three must be correctly configured for modern inbox placement.
- List hygiene: sending to email addresses that no longer exist (hard bounces) or to recipients who have not engaged in a long time signals poor list quality to ISPs. A hard bounce rate above 2 percent will damage deliverability rapidly. Remove invalid addresses, unsubscribes, and long-term unengaged contacts regularly.
- Sending volume and warm-up: new sending domains and IP addresses must be warmed up gradually. Sending large volumes immediately from a new domain triggers spam filters. A proper warm-up sequence starts with low volume (20 to 50 emails per day) and increases gradually over 4 to 8 weeks.
- Content and engagement: spam filters analyse email content for trigger words, excessive links, all-image emails, and misleading subject lines. More importantly, engagement signals (opens, replies, and clicks) tell ISPs that recipients want your email. Low engagement rates from a domain reduce deliverability over time.
- Unsubscribe compliance: in India (DPDP Act 2023), the EU (GDPR), and the US (CAN-SPAM), providing a working unsubscribe mechanism and honouring opt-out requests promptly is both a legal requirement and a deliverability best practice. High spam complaint rates from recipients who could not unsubscribe destroy sender reputation.
How to improve email deliverability for B2B cold email
- 1.Use a separate subdomain or secondary domain for cold outreach: this protects your primary business domain's reputation if your cold email reputation degrades. Example: use outreach.yourcompany.com instead of yourcompany.com for cold prospecting.
- 2.Set up SPF, DKIM, and DMARC correctly: these are table-stakes for inbox placement. Use a tool like MXToolbox or Google Postmaster Tools to verify your configuration.
- 3.Warm up new sending infrastructure: whether using a tool like Lemlist, Apollo, or Instantly, follow a structured warm-up sequence before sending at scale.
- 4.Verify email addresses before sending: use a validation tool (ZeroBounce, NeverBounce, Hunter) to remove invalid and risky email addresses before they become bounces.
- 5.Keep sending volumes consistent: sudden spikes in email volume from a domain trigger spam filters. Grow volume gradually and keep day-to-day variation modest.
- 6.Monitor your spam complaint rate: Google Postmaster Tools (free) shows your domain's spam complaint rate with Gmail recipients. A rate above 0.10 percent is a warning; above 0.30 percent triggers deliverability problems at scale.
- 7.Personalise and vary your outreach: templates sent at scale with no personalisation have low engagement rates, which over time harms domain reputation. Personalisation improves replies, which are the strongest positive engagement signal.
Email deliverability benchmarks for B2B cold email
For well-maintained B2B cold email infrastructure, target: inbox placement rate above 85 percent, hard bounce rate below 2 percent, spam complaint rate below 0.08 percent (Google's threshold), and open rate of 40 to 60 percent (noting that Apple Mail Privacy Protection inflates open rates for Apple Mail users). If your open rate has dropped significantly without a content change, deliverability is the likely culprit. Run an inbox placement test before assuming the issue is with your subject lines or messaging.
Frequently asked questions
- What is email deliverability?
- Email deliverability is the ability of an email to land in the recipient's inbox rather than their spam or junk folder. It is distinct from delivery rate (which only measures whether the email was accepted by the receiving server). In B2B cold email and marketing, poor deliverability silently suppresses campaign results because emails that land in spam are rarely opened. Deliverability is determined by sender reputation, authentication setup, list hygiene, and engagement rates.
- What is SPF, DKIM, and DMARC?
- SPF (Sender Policy Framework) specifies which mail servers are authorised to send email for your domain. DKIM (DomainKeys Identified Mail) adds a digital signature to outgoing emails that proves they were sent from your domain and have not been altered in transit. DMARC (Domain-based Message Authentication, Reporting, and Conformance) tells receiving mail servers what to do if an email fails SPF or DKIM checks, and sends reports back to the domain owner. All three must be correctly configured for good inbox placement.
- How do I check my email deliverability?
- Use these tools to diagnose deliverability: Google Postmaster Tools (free) to monitor your domain's spam rate and reputation with Gmail. MXToolbox to verify SPF, DKIM, and DMARC configuration. GlockApps or Mail-Tester to run inbox placement tests across major email providers and see where your emails land. Monitor hard bounce rates in your sending tool: anything above 2 percent needs immediate attention.
- What is email warm-up?
- Email warm-up is the process of gradually increasing the sending volume from a new domain or IP address to build a positive sender reputation before sending at scale. A new domain sent to 1,000 people on day one looks suspicious to spam filters. A structured warm-up starts at 20 to 50 emails per day and increases by 10 to 20 percent per day over 4 to 8 weeks. Warm-up tools like Instantly and Lemlist automate this by sending emails between a network of warm-up inboxes that automatically open, reply to, and unmark emails from spam.