What Is Email Marketing? | Inbound Marketing Glossary

Email marketing is a digital marketing strategy that delivers valuable content, promotions, and product information to prospects and existing customers via email to build relationships and drive conversions.

Why It Matters

Email marketing delivers the highest return on investment (ROI) of any digital marketing channel. It generates an average of $36–$40 in revenue for every $1 spent—an ROI of 3,600–4,000%. In fact, 41% of marketers cite email as their most effective marketing channel, far ahead of social media and paid search (each at 16%). Additionally, 50% of consumers report having made a purchase directly through a marketing email in the past year, demonstrating email's direct revenue impact. The global email marketing software market is projected to grow from $1.7 billion in 2025 to $4.27 billion by 2034, underscoring its continued importance.

Types of Email Marketing

Email marketing can be broadly categorized by purpose:

Newsletter: Regularly delivers industry news, blog content, and company updates to subscribers. Effective for maintaining brand awareness and building long-term trust.
Promotional email: Sent to drive sales through discounts, special offers, and new product launches. Includes a clear CTA (Call-to-Action) to prompt immediate conversion.
Transactional email: Automatically triggered by user actions such as order confirmations, shipping notifications, and password resets. This type has the highest average open rate.
Automated drip campaign: Automatically sent based on preset triggers—welcome series, onboarding sequences, cart abandonment reminders, and more. Automated emails generate 320% more revenue than non-automated emails and deliver 30x higher returns than one-time campaigns.
Re-engagement email: Sent to inactive subscribers to rekindle interest. Essential for list hygiene and deliverability maintenance.

Best Practices for Effective Emails

To produce high-performing emails, follow these principles:

Start with segmentation: Segmented email campaigns see a 30% increase in open rates and a 50% increase in click-through rates compared to non-segmented campaigns. 78% of marketers cite segmentation as their most important email strategy.
Apply personalization: Personalized emails achieve an average 29% open rate and 41% click-through rate. AI-powered personalization can boost revenue by 41% and CTR by 13.44%.
Focus on the subject line: The subject line is the first factor determining whether a recipient opens the email. Keep it short, clear, and aligned with the recipient's interests.
Mobile optimization is essential: More than half of all email recipients read emails on mobile devices. Failing to implement responsive design means losing a significant portion of your audience.
Use images: Emails with images achieve a CTR of 4.84%, roughly 3x higher than text-only emails (1.6%).

Performance Metrics

To accurately gauge email marketing performance, track these key KPIs:

Metric	Description	2025 Average Benchmark
Open Rate	Percentage of recipients who opened the email	~43.46%
CTR (Click-Through Rate)	Percentage who clicked a link in the email	~2.09%
CTOR (Click-to-Open Rate)	Percentage of openers who clicked	~6.81%
Conversion Rate	Percentage who completed the target action via email	Varies by industry
Unsubscribe Rate	Percentage who opted out	0.1–0.3%
Bounce Rate	Percentage of failed deliveries	Hard bounces: <2% recommended

Since the introduction of Apple Mail Privacy Protection, open rates may be inflated beyond actual figures. As a result, the trend has shifted toward prioritizing actionable engagement metrics such as CTR, CTOR, and conversion rate. Ultimately, the success of email marketing is best evaluated by comprehensively analyzing the entire funnel—from lead nurturing to conversion—rather than relying on any single metric.

Sources: