Email Subject Capitalization: Mailchimp vs ConvertKit for Capitalizing Email Subject Lines

Use sentence case for most email subject lines. Mailchimp gives you more built-in checks, while ConvertKit keeps the writing box simple and fast. Neither tool should decide your capitalization for you.

So, should you capitalize every word?

Usually, no.

Title Case Looks Like This. It feels polished. It can work for newsletters, sale events, and more formal brands.

Sentence case looks like this. It feels human. It often works better for creators, coaches, shops, and personal brands.

Then there is ALL CAPS. Use it like hot sauce. A tiny bit can help. Too much ruins lunch.

Here is the simple rule:

• Use sentence case for friendly, personal emails.
• Use title case for official offers, reports, or launches.
• Use all caps only for one short word, like LAST CHANCE.
• Avoid random caps, like This Sale Is SO Big. It looks spammy.

Mailchimp and subject capitalization

Mailchimp is the more “helpful parent” of the two.

When you create a campaign, Mailchimp gives you a subject line field, preview text field, and testing tools. It may also give feedback through its subject line helper features, depending on your plan and setup.

That can be useful. It can also be a little annoying.

Honestly, it feels like Mailchimp sometimes adds one more step when you just want to send the thing. You write a subject line. Then you check the preview. Then you check the helper. Then you wonder if “ends tonight” should be “Ends Tonight”. Great. Now your coffee is cold.

Still, Mailchimp is strong for teams and brands that need review steps.

Mailchimp is good for capitalization because:

• It gives you a clear place to edit the subject line.
• It supports A/B testing on many plans.
• It helps you preview how the subject may appear.
• It can flag subject lines that feel too loud or salesy.
• It works well for brands with several people checking copy.

Mailchimp is less fun because:

• The builder can feel busy.
• You may click around more than expected.
• Some useful features depend on your plan.
• It does not magically fix your capitalization taste.

Mailchimp is best if your subject lines need more review. It is also good if your boss says, “Can we test that?” every Thursday at 4:58 p.m.

ConvertKit and subject capitalization

ConvertKit, now often called Kit, is simpler.

Its email editor feels more like writing a note. That is the charm. You click. You type. You send. Nice.

For subject capitalization, this means you get fewer built-in nudges. ConvertKit will not babysit every capital letter. That is good if you know what you want. It is less good if you want the software to catch every weird-looking subject.

The catch is that simple tools make simple mistakes easier to miss. If you type “my Big NEW offer is Live”, ConvertKit may not make a fuss. Your subscribers might, though. Silently. By not opening.

ConvertKit is good for capitalization because:

• The editor is clean and quick.
• It feels natural for personal brands.
• Sentence case looks right at home.
• You can write fast without a cluttered screen.
• It is great for creator-style emails.

ConvertKit is weaker because:

• It has fewer built-in copy checks than Mailchimp.
• You need your own capitalization rules.
• Testing options can feel more limited, based on your plan and workflow.
• It will not stop you from writing a shouty subject line.

Which one wins?

For subject capitalization only, Mailchimp wins by a small margin.

Why? It gives you more tools around the subject line. Previews help. Testing helps. Extra checks help. If you are unsure whether your capitalization looks odd, Mailchimp gives you more chances to catch it.

But ConvertKit may still be the better choice for many people.

If your email voice is casual, ConvertKit feels cleaner. It does not bury you in settings. It lets you write like a human. That suits sentence case very well.

So the better answer is this:

• Choose Mailchimp if you want checks, previews, and team review.
• Choose ConvertKit if you want speed, simplicity, and a personal tone.
• Choose sentence case if you are unsure.
• Test title case only when your brand feels more formal.

Quick examples you can steal

Let’s make this practical.

Bad: HUGE SALE ON ALL OUR NEW PRODUCTS TODAY ONLY!!!

Better: Today only: 20% off new arrivals

Bad: Your Weekly Guide To Better Budgeting

Better for creators: Your weekly guide to better budgeting

Bad: we have a surprise for you

Better: We have a surprise for you

Bad: Last chance to Join Our Course Before Midnight

Better: Last chance to join our course before midnight

See the pattern? Clean wins. Normal wins. Human wins.

A simple testing plan

Do not test twenty things at once. That gets messy fast.

Use this small plan instead:

1. Pick one campaign topic.
2. Write two subject lines with the same meaning.
3. Make one sentence case.
4. Make one title case.
5. Send each to 10% of your list, if your tool allows it.
6. Send the winner to the rest.

Example:

• A: Your spring style guide is here
• B: Your Spring Style Guide Is Here

Now track three numbers:

• Open rate
• Click rate
• Unsubscribes

If sentence case gets a 38% open rate and title case gets 34%, do not overthink it. Use sentence case again. If title case wins three times in a row, your audience likes a more polished style.

The style guide I recommend

Here is a dead-simple style guide for email subject lines.

• Capitalize the first word.
• Capitalize names and brands.
• Use lowercase for most other words.
• Use one number when possible.
• Skip extra punctuation.
• Use emojis only when they match your brand.
• Keep it under 50 characters when you can.

Good examples:

• 3 ways to fix your morning routine
• Sarah, your cart is waiting
• New class starts Friday
• Last call for the workshop

These feel clear. They do not scream. They give the reader a reason to open.

Final verdict

Mailchimp is better for checking and testing subject capitalization. ConvertKit is better for writing simple, personal subject lines fast.

If you want fewer mistakes, pick Mailchimp. If you want fewer distractions, pick ConvertKit. Either way, the winning style is usually sentence case.

Do not let capital letters boss you around. Pick a style. Test it. Keep what works. Then send the email before you rename the subject line twelve more times.