Short answer: A good subject line says plainly what the email offers and matches what is inside. Mailchimp’s research points to subject lines of up to 9 words and 60 characters, with no more than 3 punctuation marks and 1 emoji. Never fake a Re: or Fwd:, and test two versions to see which one your list opens.
What the rules require
The FTC’s guide to the CAN-SPAM Act is direct: don’t use deceptive subject lines, and make the subject line accurately reflect the content of the message. The law covers all commercial email, not only bulk mail, and makes no exception for business-to-business email. Our guide to the CAN-SPAM Act covers the rest of the law, from the ad disclosure to the opt-out.
Gmail asks the same of anyone who sends to Gmail accounts. Its sender guidelines say the subject, the headers and the display name should accurately represent who sends the message and what it contains. Don’t start a subject with Re: or Fwd: unless the message really is a reply or a forward. And don’t use emojis to imitate graphic elements in a message, such as a mark next to your sender name that suggests it has been verified.
Misleading messages are one of the reasons mail ends up in spam. Our guide to why emails go to spam explains the others.
What Mailchimp’s research suggests
Mailchimp studies the emails its users send to see which practices bring the best open rates. Its tips are a useful starting point, as long as you remember they describe Mailchimp’s users, not your own list. Our email newsletter guide explains why opens are a less reliable measure than clicks.
Personalize with merge tags, using each recipient’s name or location. Be descriptive: say what the deal or the benefit is, instead of a seasonal slogan. Keep it short, with no more than 9 words and 60 characters.
Use no more than 3 punctuation marks, since too many can make an email look like spam. Use no more than 1 emoji at a time, next to words rather than instead of them, and test how it looks on different systems.
How to write and test a subject line
- Write what the email offers in plain words, as you would say it to a customer.
- Add the specific detail: the service, the discount or the date.
- Personalize it with the name or the city if your list has those fields filled in.
- Count it: up to 9 words and 60 characters.
- Trim the punctuation to 3 marks or fewer and keep 1 emoji at most.
- Check that it matches the content of the email, with no fake Re: or Fwd:.
- Send two versions in an A/B test and keep the one with the better open rate.
In an A/B test, the versions are identical except for the subject line and go to random parts of your list. Mailchimp then sends the winner to the rest. Unlike its general tips, a test tells you what your own contacts prefer.
Examples
| Instead of | Try | Why |
|---|---|---|
| “Fall into savings” | “15% off furnace tune-ups until Friday” | A specific deal says more than a seasonal slogan |
| “Re: your appointment” on a first email | “Book your spring cleaning online” | Re: only belongs on real replies |
| “HUGE SALE!!! 🔥🔥🔥” | “Our spring sale runs until Sunday 🔥” | Up to 3 punctuation marks and 1 emoji |
Our own examples, built on Mailchimp’s tips and Gmail’s sender guidelines, read on November 6, 2026.
A subject line only works if the email reaches people who asked for it. Our guide to building an email list covers how to grow one the right way.
Before you hit send
- The subject line says what the email offers, in plain words.
- It matches the content of the email.
- It has no Re: or Fwd: unless the email is a real reply or forward.
- It stays within 9 words and 60 characters.
- It has 3 punctuation marks or fewer and 1 emoji at most.
- You tested two versions on part of your list.
RememberWrite subject lines that say plainly what the email offers and match what is inside. Keep them short, go easy on punctuation and emojis, and let an A/B test show you what your own list opens.
Our email and SMS marketing service writes two campaigns a month for your list, in English, Spanish or both. Each segment gets its own subject line. Send us a WhatsApp or fill in the form.
Quick answers about email subject lines
How long should an email subject line be?
Mailchimp recommends no more than 9 words and 60 characters, based on its research into its users’ emails. Shorter subject lines often work better, especially for people who read email on their phones.
Can I use emojis in email subject lines?
Mailchimp suggests no more than 1 emoji at a time, next to words rather than instead of them, and testing how it looks. Gmail says not to use emojis to imitate graphic elements in a message, such as a mark next to the sender name that suggests it was verified.
Can I start a subject line with Re: or Fwd:?
Only on real replies and forwards. Gmail’s sender guidelines say not to use them otherwise, and the FTC’s CAN-SPAM guide says the subject line must accurately reflect the content of the message.
Should I put the customer’s name in the subject line?
Mailchimp says personalization with the recipient’s name or location increases open rates for most of its users. Use your email platform’s merge tags, and check that every contact has the field filled in.
How do I know which subject line works better?
Run an A/B test: send versions that are identical except for the subject line to random parts of your list. Mailchimp then sends the version with the best open rate to the rest, and A/B testing comes with all its paid marketing plans.
Sources
Sources read on November 6, 2026: Best Practices for Email Subject Lines (Mailchimp Help). Email sender guidelines (Gmail Help). CAN-SPAM Act: A Compliance Guide for Business (Federal Trade Commission).