Subject lines are the highest-leverage copy you write. They also affect complaint rates, which feed reputation.
Mistake 1: Clickbait that produces opens but drives complaints and unsubscribes#
Why it hurts: this undermines email subject lines at the point where mailbox providers make their decision, and it is rarely surfaced by your own tooling until placement drops.
Fix: Keep subject lines under 50 characters so they survive mobile truncation.
Mistake 2: All-caps and excessive punctuation, which pattern-match to spam#
Why it hurts: this undermines email subject lines at the point where mailbox providers make their decision, and it is rarely surfaced by your own tooling until placement drops.
Fix: Write the preheader as a continuation, not a repeat of the subject.
Frequently asked questions#
Do emojis in subject lines hurt deliverability?
Not directly. They can hurt engagement with B2B audiences and render inconsistently across clients.