Email deliverability is the measure of whether your emails successfully reach the recipient's inbox rather than bouncing, being rejected, or landing in spam. It's determined by a combination of sender reputation, email authentication, content quality, and list hygiene. A 95% deliverability rate means 5 out of every 100 emails you send never reach anyone.
Why It Matters
You can write the best email in the world, but it doesn't matter if it never arrives. Poor deliverability is often invisible: your email platform shows "sent" but 20% of those messages hit spam or get silently rejected. Your open rates look low, your reply rates look terrible, and you blame the copy when the real problem is that half your list is outdated. ISPs penalize senders who consistently hit bad addresses, and recovery takes weeks.
Factors That Affect Deliverability
- List quality: Bounce rate is the #1 factor. Sending to invalid addresses tells ISPs you don't maintain your list
- Sender reputation: ISPs assign a score to your sending domain and IP. High bounces, spam complaints, and low engagement lower it
- Email authentication: SPF, DKIM, and DMARC records prove your emails are legitimate. Without them, you look like a spammer
- Engagement rates: ISPs track opens, clicks, and replies. Low engagement signals that recipients don't want your emails
- Spam traps: Old, abandoned email addresses that ISPs monitor. Sending to them proves you're not cleaning your list
Example
A company's cold email reply rate drops from 4% to 0.5% over three months. Investigation reveals their sender reputation score dropped from 85 to 42 because 18% of their list was invalid addresses accumulated over two years. They clean the list, remove 3,400 bad addresses, warm up a new sending domain, and reply rates recover to 3.5% within six weeks.
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