The subject line and preheader are the two text fields shown in the inbox list before a message is opened. They determine whether a recipient opens, ignores, or reports the message.
What good looks like#
- Done: Keep subject lines under 50 characters so they survive mobile truncation.
- Done: Write the preheader as a continuation, not a repeat of the subject.
- Done: A/B test one variable at a time with a statistically meaningful sample.
- Done: Avoid deceptive 'Re:' or 'Fwd:' prefixes, which violate CAN-SPAM and raise complaints.
What bad looks like#
- Seen in audits: Clickbait that produces opens but drives complaints and unsubscribes.
- Seen in audits: All-caps and excessive punctuation, which pattern-match to spam.
How to move from bad to good#
Work through the good list in order and re-verify after each change. Most teams find one or two items from the bad list already present; fixing those usually produces the largest improvement.
Frequently asked questions#
Do emojis in subject lines hurt deliverability?
Not directly. They can hurt engagement with B2B audiences and render inconsistently across clients.