Subject lines

Your subject line is the first thing subscribers see in their inbox. This article covers how to set it up and choose the right strategy.

Where to find it

Go to Messaging → [Your Newsletter] → Email tab. The Subject & Preview card is at the top.

Three subject line strategies

You'll see a Subject Line Source dropdown with three options:

1. Selected Article

Uses the title of the top article in a section you choose. Best when:

• You want fresh, content-driven subject lines automatically
• You don't want to write a new subject for every send
• The first article in your chosen section will reliably make a good subject

You'll set Section for Subject to tell rasa.io which section's top article to use.

2. Featured Article

Uses a featured article's title as the subject. Best when:

• You want consistent control over what drives the subject
• You feature a different article each send to highlight specific content
• The featured article is always your "pick of the week"

This is useful when you want editorial control without writing a new subject every time.

3. Custom

Write your own subject line every time. Best when:

• You want full creative control
• You're testing different subject styles
• The article-based subjects don't fit your brand voice

If you go custom, you can use merge tags (see below) to inject personalization.

Date format

Choose how dates appear in your subject line. You'll see six format options — pick the one that fits your brand. Examples:

• Long: "Monday, May 27, 2026"
• Short: "May 27"
• Numeric: "5/27/2026"

The date format applies to date merge tags in your subject and preview text.

Preview text

Below the subject field, you'll see Preview Text — the snippet that appears in subscribers' inboxes next to the subject (in Gmail, Outlook, etc.).

If you don't set this, inbox providers will pull from the first text in your email — usually not what you want. Set a custom preview text to:

• Reinforce or extend the subject line
• Tease specific content
• Increase open rates

Aim for 35-90 characters for preview text; anything longer gets cut off by most inbox previewers.

Merge tags

Click any merge tag chip below the subject field to insert a dynamic value. Common merge tags:

• Subscriber first name
• Subscriber company
• Current date
• Newsletter name

For example, a subject like "Your weekly digest, " becomes "Your weekly digest, Alex" for Alex and "Your weekly digest, Maria" for Maria.

Subject line best practices

• Keep it short — 40-50 characters is the inbox sweet spot
• Lead with the value — what's in it for the reader?
• Avoid spammy words — "free," "act now," excessive capitalization, and lots of punctuation can hurt deliverability
• Test variations — send tests to yourself with different subjects to see what reads best
• Personalize when relevant — first name is fine, but only when it adds value

Tips by strategy

If using Selected Article:

• Make sure your top section is the strongest content
• Use sections to organize so the "lead" content surfaces predictably

If using Featured Article:

• Feature a different article each send for variety
• The first featured article in your pool typically becomes the subject

If using Custom:

• Keep your tone consistent across sends
• Mix in seasonal or topical references when appropriate

What's next

• Sending test emails and previewing — review how your subject looks before sending
• Curating content — how to feature articles