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Subject & AI subject lines

The subject line is the first thing a recipient sees and the biggest lever on your open rate. Write your own, or let EmailFlow AI generate a set of options tailored to your email's content.

AI-generated subject lines

Rather than staring at a blank field, ask the AI for ideas. It reads your email and proposes several subject-line options in different styles — curiosity-driven, benefit-led, urgent, or playful. Pick the one you like, edit it, or regenerate for more. It's the fastest way to break writer's block and test different angles.

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Generating subject lines uses a small amount of your AI token allotment — far less than building a full email.

What makes a strong subject

  • Be specific. “Your March report is ready” beats “Newsletter.”
  • Keep it short. Many inboxes truncate after ~40–50 characters, especially on mobile.
  • Front-load value. Put the most compelling word first.
  • Match the content. Misleading subjects spike unsubscribes and complaints.

Preview text

The preview (or preheader) text is the snippet shown next to or under the subject in most inboxes. Treat it as a second subject line: use it to extend the hook rather than repeat it. A strong subject plus complementary preview text noticeably improves opens.

Test it with A/B

Not sure which subject will win? Don't guess — run an A/B test. Send competing subject lines to a slice of your audience, let EmailFlow AI measure open rates, and have it automatically send the winner to everyone else.

Subject-line mistakes to avoid

  • Clickbait. Over-promising spikes opens but tanks trust and drives unsubscribes and spam complaints.
  • ALL CAPS and excessive punctuation. They look spammy and can hurt deliverability.
  • Vague subjects. “An update” gives no reason to open; be concrete.
  • Ignoring the preview text. Leaving it empty wastes prime inbox real estate.

Frequently asked questions

How long should a subject be? Aim for around 40–50 characters so it isn't truncated on mobile, and front-load the most important words.

Do emojis help? Used sparingly and on-brand, an emoji can add personality — but test it with A/B testing rather than assuming, since results vary by audience.