A/B Subject Line Testing
Small subject line tweaks can 2x your open rates. Muzero lets you test up to 5 subject line variants per campaign — then automatically sends the winner to the remaining audience.
A/B Subject Line Testing
Campaign Automation
Up to 5
Variants
Auto
Winner selection
AI
Suggestions
Why teams use this
Data-driven subjects
Stop guessing which subject line works — test and know for sure.
Automatic optimization
Winning variant is automatically sent to the remaining audience.
AI-assisted
AI generates variant suggestions based on your email content and audience.
What's included
Set up in 3 steps
Get started in minutes — no engineering required.
Write your variants
Enter 2–5 subject line options — or let AI generate variants for you.
Set test parameters
Choose test audience size and minimum send count for significance.
Winner takes all
Once a winner is found, the remaining audience gets the best-performing subject.
Who it's built for
Growth teams
Systematically optimize open rates across every campaign
Agencies
Prove to clients which messaging resonates with data-driven results
Product launches
Test angle, urgency, and curiosity-driven subject lines before full send
Common questions
Everything you need to know about A/B Subject Line Testing.
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