Should Email Subject Lines Be Capitalized? Title Case vs Sentence Case

Capitalize the first word of every subject line. After that, it's a style choice, and one style reads more like a person.

Use sentence case for most email subject lines: capitalize the first word and any proper nouns, and leave everything else lowercase. In our view it reads like a note from a person, while title case reads like a headline from a brand. Whichever you pick, use it consistently, and never write a whole subject line in capitals.

This is the short answer on capitalization in email subject lines.

Yes, capitalize the first word. Beyond that, sentence case is the safer default for email, for three reasons:

• It looks like a personal email. People write to each other in sentence case. A subject line in title case looks like a newsletter or an ad before anyone reads a word.

• It's what the big tech style guides use for headings. Microsoft and Google both default to sentence case for titles and headings (details below), though APA and Chicago still use title case.

• It's easier to get right. Title case has rules about which short words stay lowercase, and those rules differ between style guides. Sentence case has one rule.

Title case isn't wrong. It can suit a formal announcement or a brand that uses it everywhere. The mistake is switching between the two from one email to the next.

Here are the same subject lines in both styles.

These are original examples from our lists of email subject lines and business email subject lines. The title case column follows the Chicago Manual of Style's 18th edition rules (explained below). Capitalization doesn't change the character count.

Read the two columns aloud. The left sounds like someone telling you something; the right sounds like a sign.

Watch the details in title case. "For", "in" and "from" stay lowercase under Chicago, but "From" would be capitalized under AP's rule for titles of works, which capitalizes words of four letters or more, prepositions included (Editor's Manual). And "Up" in "Set Up" is capitalized because Chicago capitalizes prepositions used as adverbs, which "up" is there (CMOS Shop Talk). Sentence case avoids those judgment calls.

This is what style guides recommend.

No style guide covers email subject lines directly, but they all cover titles and headings, and a subject line is an email's title.

Microsoft also uses sentence case for blog post and press release titles, keeping title case for things like product names and book titles (Microsoft). Email is closer to a blog post.

News writing leans the same way. The AP Stylebook is subscription-only, but Writing Explained's summary of AP style says that "only the first word and proper nouns are capitalized in headlines" (Writing Explained).

If you do choose title case, pick one guide and follow it. The rules that trip people up:

• Articles (a, an, the) stay lowercase unless they're the first word (APA and Microsoft both say so).

• Short prepositions depend on the guide. APA lowercases conjunctions and prepositions of three letters or fewer (APA). Microsoft lowercases prepositions of four letters or fewer. Chicago 18 lowercases prepositions under five letters.

• After a colon, Microsoft and APA both capitalize the first word. That's worth copying in sentence case too: "Last call: Free returns end tonight" reads as two clear parts.

This is when capital letters hurt deliverability.

Title case versus sentence case is a question about readers. For deliverability, the question is all caps.

A subject line written entirely in capitals is a known spam signal, but a small one on its own. SpamAssassin, the open-source filter, has a rule for a subject that is all capitals, scored at 0.5 points, against a default spam threshold of 5 (rule scores, default threshold). Filters add signals up, so all caps plus "!!!" plus a sender with a weak reputation is where trouble starts. Litmus also warns that all caps and exclamation points are often associated with spam emails and can harm your sender reputation (Litmus).

The bigger cost is with readers. All caps reads as shouting, and Microsoft's guide says plainly: "Don't use all uppercase for emphasis" (Microsoft). Annoyed readers hit the spam button, and complaints count for more than any single word. Google asks senders to keep their reported spam rate below 0.3%, and recommends staying below 0.1% (Google).

What's fine:

• Acronyms and codes that are always written in capitals: "Your PDF is ready", "Use code SPRING15".

• Proper nouns with their own styling, like product names.

• One capitalized word, sparingly, if your brand voice calls for it.

Here is how to test it on your own list.

To see whether case matters to your readers, send the same email with two subject lines that differ only in case to two random halves of one audience, and compare click rates rather than opens. In Spreeflo that's a Random Split step with a Send Email on each path, on the Starter plan. In our experience wording matters more than case, so we'd test wording first.

Build this in Spreeflo

Write your subject lines once in the style you choose, save them in reusable email templates, and test wording with Random Split before you roll it out to the whole list. Spreeflo Starter starts at $16 a month.

Try the journey builder, no login → · See pricing

Common questions

Should email subject lines be capitalized?

Capitalize the first word and any proper nouns. For the rest, sentence case (lowercase, like a normal sentence) suits most marketing and work emails because it reads as personal. Title case is acceptable if you use it consistently, but avoid writing a whole subject line in capitals.

Do you capitalize every word in an email subject line?

No. Even in title case, short words usually stay lowercase: articles like "a" and "the", and short prepositions such as "for", "in" and "from" under Chicago. APA lowercases prepositions of three letters or fewer, and Microsoft four or fewer. In sentence case you capitalize only the first word and proper nouns. Never capitalize every letter.

Is title case or sentence case better for email?

Sentence case is the better default. Microsoft's and Google's style guides use it for titles and headings, it has only one rule to follow, and it looks like an email from a person. Title case can work for formal announcements or brands that use it everywhere else.

Do all-caps subject lines go to spam?

Not on their own, but they add to the spam score. SpamAssassin scores an all-caps subject at 0.5 points against a default threshold of 5, and Litmus notes that all caps are often associated with spam. Combined with heavy punctuation or a weak sender reputation, it can tip an email into the junk folder.

Read these next

• Email subject lines: 150+ examples sorted by the job they do

• Business email subject lines: 80 examples for every kind of work email

• Sales email subject lines: 60 that get demos booked

• Promotional email subject lines: 70 for launches, discounts and last chances

Sources

• Microsoft Writing Style Guide: Capitalization, read 27 October 2026

• Google developer documentation style guide: Capitalization, read 27 October 2026

• APA Style: Title case and Sentence case, read 27 October 2026

• CMOS Shop Talk: Announcing The Chicago Manual of Style, 18th Edition, read 27 October 2026

• CMOS Shop Talk: Chicago Style Workout 29, read 27 October 2026

• Editor's Manual: Title case, read 27 October 2026

• Writing Explained: AP style headlines, read 27 October 2026

• Apache SpamAssassin default rule scores and default preferences, read 27 October 2026

• Litmus: Email subject line best practices, read 28 October 2026

• Google: Email sender guidelines, read 27 October 2026