Email Marketing Glossary: Open Rate, Deliverability & More Explained

By Ajay Maheshwari · Updated Jul 29, 2026

Written by Ajay Maheshwari

Founder, Diginex-US

5+ Years SEO Digital Marketing Certified Data Science Trained

Ajay Maheshwari is the founder of Diginex-US, with 5+ years of hands-on experience in SEO, including international freelance projects for clients across multiple countries. He holds a Digital Marketing certification and has pursued formal training in Data Science.

Every email platform — MailerLite, Kit, ActiveCampaign, Mailchimp — reports the same core metrics, but the terminology can be confusing if you're new to email marketing. Here's what each one actually means, and what a healthy number looks like.

Delivery & Deliverability Terms

Deliverability: The percentage of emails that actually reach a subscriber's inbox, as opposed to bouncing or landing in spam. This is affected by your sender reputation, list quality, and email content — not just whether the platform "sent" it.
Bounce Rate: The percentage of emails that failed to deliver. A hard bounce means the address doesn't exist; a soft bounce is usually temporary (full inbox, server issue). Bounce rates above 2% start to hurt your sender reputation.
Sender Reputation: A score email providers (Gmail, Outlook) assign to your sending domain based on past behavior. Poor reputation means more of your emails land in spam regardless of content quality.

Engagement Terms

Open Rate: The percentage of delivered emails that were opened. Industry average sits around 20-25%, though this metric has become less reliable since Apple Mail Privacy Protection began pre-fetching images, inflating open rates artificially.
Click-Through Rate (CTR): The percentage of recipients who clicked a link inside the email. This is generally considered a more reliable engagement signal than open rate, since it requires genuine action.
Click-to-Open Rate (CTOR): Clicks divided by opens (not by total sent) — this isolates how compelling your email content is, separate from how good your subject line was at getting the open.

List Health Terms

Unsubscribe Rate: The percentage of recipients who opted out after a given send. Under 0.5% is healthy; consistently higher suggests a mismatch between what you promised subscribers and what you're sending.
List Segmentation: Dividing your subscriber list into smaller groups based on behavior, purchase history, or interests, so you send more relevant emails to each group instead of one generic blast to everyone.
Inactive/Dormant Contacts: Subscribers who haven't opened or clicked in an extended period (often 90-180 days). This matters directly for cost — some platforms bill based on total contacts including inactive ones, which is a real pricing trap worth checking before you sign up.

Why this matters for pricing: Our Mailchimp review covers exactly this issue — Mailchimp bills for inactive contacts unless you manually archive them, while MailerLite and Kit don't have this same reported issue.

Frequently Asked Questions

What's a good open rate for email marketing?

Industry averages sit around 20-25%, though this varies significantly by industry and has become less reliable as a metric since Apple Mail Privacy Protection began affecting open tracking.

Why is my bounce rate important?

A high bounce rate damages your sender reputation, which makes future emails more likely to land in spam — even for engaged subscribers who want to hear from you.

Should I remove inactive subscribers from my list?

Generally yes, especially on platforms that bill by total contact count. Removing genuinely inactive subscribers also improves your engagement metrics and sender reputation.