Using subject lines like "Verify your active status" can lift open rates by 27-31% for contacts who haven't engaged in over a year. While effective for reactivation, this slightly gimmicky approach will also annoy some users, leading to a higher-than-usual unsubscribe rate and negative replies, which requires 'thick skin'.

Many marketers mistakenly summarize their entire email in the subject line, removing any incentive to open it. To increase curiosity, provide only a hint or a compelling data point from the email's content. This creates an information gap that subscribers feel compelled to close by clicking.

Engage sophisticated audiences by telling them an email is *not* for them. Subject lines like "not for advanced marketers" or "ignore this if your conversions are strong" subconsciously challenge their expertise and ego, compelling them to open the email to prove the statement wrong.

While acknowledging it was a tactic used over a decade ago in sales emails, marketers now unequivocally label using "RE:" in a subject line for a non-reply email as "total, absolute garbage." This reflects a shift towards more authentic and less deceptive marketing practices.

Contrary to old email marketing wisdom, testing fully capitalized subject lines can significantly increase open rates by 3-4 percentage points. Modern spam filters are less likely to penalize this tactic, making it a viable test for grabbing attention in a crowded inbox.

For subscribers who don't open an email, a simple and effective tactic is to resend the exact same content. The only change is tweaking the subject line and pre-header to capture their attention. Since they never saw the original content, it's still new to them and requires minimal effort to redeploy.

Marketer Jay Schwedelson argues that non-openers are distracted, not disinterested. He advises resending the same email within 48 hours but with a new, aggressive subject line that creates urgency (e.g., 'Yikes, you scrolled past this'). This gives the message a second chance to cut through the inbox noise.

Many marketers mistakenly reveal the entire value of an email in the subject line, killing any reason to open it. To maximize opens, provide a compelling hint or create a curiosity gap rather than giving away the full story.

Contrary to old marketing beliefs, using all capital letters in a subject line can significantly increase open rates without negatively impacting deliverability. It's a simple test many marketers avoid due to outdated fears of spam filters.