Writing clear, authentic subject lines helps your marketing emails land directly in your contacts' inboxes rather than the spam folder. Subject lines heavily influence email deliverability because mailbox providers analyze formatting, keyword patterns, and subscriber engagement to decide message placement.
Keep punctuation simple by using no more than one exclamation mark and avoiding decorative characters like "$$$" or "???".
Spam filters assign higher risk scores to messages with stacked punctuation marks. According to email scoring researches excessive punctuation like "!!!" or "???" triggers high-risk spam filter flags that reduce inbox placement.
Avoid: "Unbelievable offer today only!!!!!! $$$"
Recommended: "Your seasonal discount is ready"
Add contact attributes, such as first names, into the subject line using dynamic content.
A benchmark study found that personalized subject lines are 26% more likely to be opened. When contacts consistently open your emails, mailbox providers recognize your domain as trusted, helping your messages land in the inbox.
Avoid: "Here is your monthly newsletter"
Recommended: "{{ receiver.last_name }}, here are your monthly updates"
Write subject lines in standard sentence case or title case. Avoid writing full words in ALL CAPS and remove words like "test", "100% free", or "guaranteed".
ALL CAPS text looks like shouting and matches known spam patterns. Modern spam scoring engines flag ALL CAPS words as high risk. Words like "test" are also flagged because automated spam testing scripts use them frequently. Keeping copy natural keeps your risk score low.
Avoid: "TEST CAMPAIGN: CLAIM YOUR FREE GIFT NOW"
Recommended: "Here is your updated feature preview"
Include a single relevant emoji (or up to two for consumer brands) placed naturally near the end of your subject line.
A single emoji adds visual contrast in crowded inboxes to grab attention without taking up extra character space. Research shows that subject lines with emojis can boost unique open rates by up to 56%. Higher open rates signal to mailbox providers that contacts want your emails, which improves deliverability over time. However, stacking multiple emojis triggers spam filters and increases contact unsubscribes.
Avoid: "π₯ππ BIGGEST SALE OF THE YEAR πππ₯"
Recommended: "Your weekly digest is here π"
Keep your subject line concise, aiming for 28 to 40 characters (around 6 to 10 words).
Over 60% of emails are opened on mobile devices, where subject lines truncate after 36 to 41 characters. According to various researches, subject lines between 28 and 39 characters generate the highest click-through rates because contacts can read the full hook without clipping.
Avoid: "We wanted to take a moment to inform you about all our brand new workspace additions for this month"
Recommended: "See what is new in your workspace"
A/B testing lets your team send two different subject lines to a small portion of your contacts to see which one performs best before reaching your full audience. Testing takes the guesswork out of email copy, helping you learn what phrasing, tone, or emojis resonate with your contacts.
To evaluate your results, compare the open rates of both versions after a few hours - the option with the higher open rate shows stronger contact interest and better inbox placement.
More about A/B tests in βHow to A/B Test Email Campaignsβ.
Always align your subject line copy directly with your email content and landing page offer. Mailbox providers monitor recipient reactions after opening. Misleading subject lines lead to high unsubscribe and spam complaint rates, which damages domain reputation and deliverability.
