Definition
Subject line capitalisation affects how your email appears in the inbox and may influence open rates. The two main styles are sentence case ("This is a subject line") and title case ("This Is a Subject Line"). All caps should be avoided as they trigger spam filters.
Which Performs Better
There is no universal winner — it depends on your brand voice and audience. Sentence case feels more natural and conversational, which works well for B2B and educational content. Title case can appear more formal or authoritative, which may suit promotional offers and news.
Testing Recommendations
A/B test capitalisation on your own audience. Use sentence case for the control and title case for the variant. Run the test until you reach statistical significance. Some senders find that sentence case outperforms by 5-15% for engagement-focused campaigns.
Related Glossary Terms
A/B Testing
A/B testing in email marketing is the practice of sending two variations of an email to a small sample of your list to determine which version performs better before sending the winner to the remaining subscribers.
Abandoned Cart Email
An abandoned cart email is an automated message sent to customers who added items to their online shopping cart but left without completing the purchase. It is one of the highest-converting email types in ecommerce.
AIDA Model for Email
The AIDA model (Attention, Interest, Desire, Action) is a classic copywriting framework used to structure email campaigns that guide subscribers from awareness to conversion.
AMP for Email
AMP for Email is a Google-developed framework that allows email messages to include interactive elements like forms, carousels, accordions, and live content. It turns static emails into dynamic, interactive experiences directly inside the inbox.
Anchoring Effect in Email Marketing
The anchoring effect is a cognitive bias where the first piece of information presented (the anchor) influences subsequent decisions, used in email to frame pricing and value perception.
Announcement Email
An announcement email is a dedicated campaign that communicates a specific update, milestone, or change to subscribers, from product launches and feature releases to company news and events.