Email Marketing Terms Explained
Glossary of key email marketing metrics and frequently asked questions.
Glossary of Key Terms
AOV (Average Order Value)
The average amount a customer spends each time they make a purchase. In email ROI calculations, this is multiplied by the number of conversions to estimate revenue.
Bounce Rate
The percentage of emails that were not delivered to recipients' inboxes. Hard bounces (invalid addresses) and soft bounces (temporary issues like full inbox) are tracked separately.
CTR (Click-Through Rate)
The percentage of email recipients who clicked on at least one link in your email. Calculated as (Unique Clicks / Emails Delivered) × 100. Industry average is 2.5%.
Conversion Rate
The percentage of clicks that result in a desired action (purchase, signup, download). Calculated as (Conversions / Unique Clicks) × 100. Industry average is 1.5%.
Deliverability
The percentage of emails that successfully reach recipients' inboxes (not spam folders). Industry average is 83%, but a well-maintained setup should achieve 93%+.
DMARC
Domain-based Message Authentication, Reporting & Conformance. An email authentication protocol that helps prevent email spoofing and improves deliverability.
ESP (Email Service Provider)
A company that offers email marketing services, including sending infrastructure, template design, automation, and analytics. Examples: Mailchimp, Klaviyo, Brevo.
List Decay
The natural rate at which email lists lose valid subscribers due to email address changes, job changes, or disengagement. Average rate is 22.5% per year (HubSpot).
List Hygiene
The practice of regularly cleaning your email list by removing invalid, unengaged, or risky addresses to maintain good deliverability and accurate metrics.
MPP (Mail Privacy Protection)
Apple's privacy feature that automatically loads remote content in the background, inflating open rates for Apple Mail users by an estimated 5-10%.
Open Rate
The percentage of delivered emails that were opened. Calculated as (Unique Opens / Emails Delivered) × 100. Cross-industry average is 22%.
ROI (Return on Investment)
In email marketing, ROI measures profitability as (Revenue - Total Cost) / Total Cost × 100. Average email marketing ROI is 3,600% ($36 per $1 spent).
Sender Reputation
A score ISPs assign to email senders based on sending volume, complaint rates, bounce rates, and engagement. A poor reputation leads to spam filtering.
SPF / DKIM
Email authentication protocols that verify your domain is authorized to send emails. Proper setup improves deliverability and prevents spoofing.
CTOR (Click-to-Open Rate)
The percentage of unique opens that resulted in at least one click. Calculated as (Unique Clicks / Unique Opens) × 100. Considered a more reliable engagement metric than open rate alone, especially since Apple's MPP inflates open data.
CAN-SPAM Act
US law regulating commercial email. Requires accurate headers, clear subject lines, a physical address, and an opt-out mechanism in every commercial email. Violations can result in fines of up to $50,120 per email.
GDPR
General Data Protection Regulation — EU law requiring explicit consent for email marketing, clear privacy policies, and the right to be forgotten. Applies to any business sending emails to EU residents, regardless of where the business is based.
Segmentation
Dividing your email list into smaller groups based on shared characteristics such as purchase history, engagement level, demographics, or behavior. Segmented campaigns generate up to 760% more revenue than non-segmented broadcasts (Campaign Monitor).
Whitelisting
When a subscriber adds your email address to their address book or contacts list. Emails from whitelisted senders are less likely to be filtered as spam, improving deliverability rates for future campaigns.
A/B Testing (Split Testing)
Sending two variations of an email to a small sample of your list to determine which performs better, then sending the winning version to the remaining subscribers. Common variables include subject lines, CTAs, send times, and content layout.
Transactional Email
Emails triggered by a user action such as a purchase, password reset, or account signup. Transactional emails have higher deliverability expectations than marketing emails and are exempt from CAN-SPAM opt-out requirements.
Warm-Up
The process of gradually increasing email sending volume from a new domain or IP address to build sender reputation with ISPs. A proper warm-up takes 2-4 weeks and is essential before launching cold email campaigns from a new domain.
Frequently Asked Questions
What is email marketing ROI?
Email marketing ROI (Return on Investment) measures the profit you generate from email campaigns relative to what you spend. The formula is: (Revenue - Total Cost) / Total Cost × 100. The average email marketing ROI across all industries is 3,600%.
How is email revenue calculated?
Email revenue is calculated by multiplying: Monthly Volume × Deliverability Rate × Open Rate × CTR × Conversion Rate × Average Order Value. Each step in the funnel reduces the pool, so small improvements at the top compound significantly.
What is a good email open rate in 2026?
The cross-industry average open rate is 22%. Rates above 25% are considered good, and above 30% are excellent. Note that Apple's MPP may inflate reported open rates by 5-10%.
How much can I save by switching ESPs?
Savings vary by provider and subscriber count. For a 50,000-subscriber list, switching from Mailchimp ($59/mo) to Brevo ($25/mo) saves $408/year. Switching from ActiveCampaign ($229/mo at 50k) to ConvertKit ($119/mo) saves $1,320/year. Use our ROI calculator for your specific numbers.
What is the average deliverability rate?
The industry average deliverability rate is 83% (Campaign Monitor). However, a well-maintained email setup with proper authentication, good list hygiene, and a positive sender reputation should achieve 93-97% deliverability.
Is this calculator free to use?
Yes, the Open-rate.com Email Marketing ROI & Savings Calculator is completely free to use. No registration or login required. You can use it as many times as you want.
How accurate is the ROI calculator?
The calculator uses standard ROI formulas and industry benchmark data. Its accuracy depends on the accuracy of your inputs. For best results, use your actual campaign data rather than industry defaults. The calculator is designed for educational and planning purposes.
Is email marketing still worth it in 2026?
Yes, email marketing remains the highest-ROI digital marketing channel in 2026, generating an average of $36 for every $1 spent. Unlike social media (where organic reach is below 5%) and paid ads (where CPC increased 15% in 2025), email gives you direct access to an audience you own with no algorithm gatekeeping.
How many emails should I send per week?
Optimal frequency depends on your industry. E-commerce can sustain 3-4 emails per week, B2B SaaS should send 1-2 per week, content publishers can send daily (5-7x), and service businesses should send 1x per week. The key metric is revenue per send -- if adding an email reduces revenue per send by more than 30%, you are sending too much.
How much does email marketing cost per month?
ESP costs range from $0-50/month for small lists (under 5,000 subscribers) to $200-2,000/month for larger lists (50,000+ subscribers). However, the true cost includes labor (15-25 hours/week for a small business), tools ($150-1,000/month), and content creation. Total monthly cost typically runs $500-5,000 for most businesses.
What is a good unsubscribe rate?
A healthy unsubscribe rate is below 0.3% per email send. Rates between 0.3-0.5% are acceptable but indicate possible content or frequency issues. Above 0.5% per send is a red flag -- you are losing more than 2% of your list monthly, which outpaces most growth efforts.
How do I set up SPF, DKIM, and DMARC?
Add an SPF TXT record to your DNS listing your ESP's sending servers, generate DKIM keys in your ESP and add the public key to DNS, and create a DMARC TXT record starting with p=none to collect data. Most ESPs provide step-by-step setup guides. After 30 days, evaluate moving to p=quarantine or p=reject.
What is the average email list churn rate?
Email lists naturally decay at approximately 22.5% per year (HubSpot data) due to email address changes, job moves, and disengagement. A list of 10,000 subscribers loses about 2,250 addresses annually. Clean your list quarterly and grow by 2%+ monthly to maintain size.
Can I buy an email list?
No. Bought lists have near-zero engagement, high spam complaint rates, and violate CAN-SPAM and GDPR regulations. Build your list organically through opt-in forms, lead magnets, and content marketing. The ROI of an organic list is 10-50x higher than a bought list.
How long should an email be?
Promotional emails: 50-125 words. Newsletters: 200-500 words. Educational content: 500-1,000 words. Every word should earn its place. B2B audiences tolerate longer emails than B2C. Test different lengths with your audience.
What is the best ESP for small businesses?
MailerLite for creators (best free tier), Klaviyo for e-commerce (Shopify integration), Brevo for budget-conscious (cheapest at scale), Mailchimp for beginners (easiest to use). Compare options on our best ESP comparison page.