Email Subject Line Capitalization Tool

Which case to use

Use sentence case for most emails. Only the first word and names get a capital. It reads like a normal email from a person, so it's what we'd pick for one-to-one emails, replies and mail merges. Title case, with a capital on most words, looks like a headline. It fits formal notes and newsletters. Either way, don't switch styles from one email to the next.

The Chicago Manual of Style, a writing guide, draws the same line. The book doesn't cover subject lines, but its editors say that for personal messages, even about work, “sentence case would usually be appropriate”. Chicago's version of title case, they say, fits formal messages sent by an organization that otherwise follows Chicago style.

Whatever you pick, don't type the whole line in capitals. It reads as shouting, and capital letters may trigger spam filters.

What the tool changes, and what it leaves alone

Sentence case gives a capital to the first word, and to the first word after a colon, a dash or the end of a sentence. Every other word is lowercase. The first-word rules follow APA style, and Google's style guide also uses sentence case. If your line mixes capitals and lowercase words, the capitals in the middle stay, because they're probably names. If your line is typed in title case, the tool lowercases those capitals.

Title case gives every word a capital except a, an, the, short conjunctions (and, as, but, for, if, nor, or, so, yet) and short prepositions (at, by, in, of, off, on, per, to, up, via, vs). The same first words as in sentence case always get one, and so does the last word. These are APA's title case rules, with “vs” and the last word added.

Both cases keep these:

• Markers in all three YAMM formats: {{First name}}, <<First name>> and $%First name%.
• Words with a capital after the first letter, like YAMM, PDF, iPhone and eBay, unless the line is shouting: two or more words in capitals and no lowercase words, or three or more words in capitals that make up most of the line.
• Words with a number, like Q3 or 2FA, and links and email addresses.
• Re:, Fwd: and Fw: at the start (the reply and forward labels). They get a capital, and the word after them counts as the first word.

The tool can't know every name. It always capitalizes Gmail, Google, Outlook, YAMM, the days and the months (but not May, which is also a verb). When you switch a title case line to sentence case, any other name loses its capital: “Lunch With Rose on Friday” becomes “Lunch with rose on Friday”. Sorry, Rose. Read the result before you copy it.

If your company follows Chicago style, fix two kinds of words by hand. APA capitalizes any word of four letters or more, so the tool gives “with” and “from” a capital. Chicago lowercases prepositions of four letters. And Chicago capitalizes “Up” when it's an adverb that goes with a verb, as in “Dress Up”. The tool can't tell when “up” belongs to a verb, so “sign up for our webinar” comes out “Sign up for Our Webinar”.

Does capitalization change open rates?

Not in a way you can count on. The two studies we found point in opposite directions, and neither is a controlled test (a test that changes only the capitalization):

So pick the case that fits the email, not the one a study liked. If you test both on your own list, compare replies, not opens.

Capitalization in a mail merge subject

YAMM is a mail merge for Gmail and Google Sheets, installed more than 16 million times. It sends everyone on your list their own copy of one Gmail draft, from your own Gmail account, so the draft's subject is the subject of every email. Markers work in the subject too, and YAMM matches a marker to its column in upper or lower case: {{first name}} finds a First Name column in your sheet. So the tool leaves markers as you typed them: in YAMM, their case changes nothing.

To see the real subject with a recipient's details in it, send yourself a test email. YAMM fills in the markers from the first visible row of your sheet.

Planning a follow-up in the same thread? It needs the same subject line as the first email, so settle the capitalization before the first send.

Need subject ideas first? Try the AI subject line generator. To send your first mail merge, install YAMM and follow our guide to sending personalized mass emails from Gmail.