How Should You Capitalize Your Email Subject Lines?

6 min readApr 20, 2021


One of the most fiercely debated areas in email subject lines is the topic of capitalization. Do you capitalize major words as if it’s the title of a novel? Or do you capitalize like it’s a sentence? What about all caps? What about no caps?

These are the options that every marketer faces when they write a subject line. There are pros and cons to each method, but it’s really more about brand preference. Just make sure, whatever you pick, that you are consistent in your usage. It’s more than just adhering to a made-up guideline, it becomes part of the voice of your brand.

Let’s go through each of the available options and examine where each option fits into your email marketing strategy.


Honestly, this is the only option that I would say is the wrong option. Don’t use capitalize every word in your subject line. IT’S LIKE YELLING. There are some organizations that get away with it, even some that say they get great results when they A/B tested all caps over other formats.

But believe me. It’s too risky. Overusing capitalization in your subject lines will make you look shady (especially in B2B) and, on top of that, it will trigger spam filters. Even capitalizing one full word in your subject lines significantly increases the chance that your email will go straight to spam without the recipient ever seeing it.

Nobody wants that. Don’t risk it.


To pull off this option, capitalize the first word and any proper nouns. Just like if you were writing a sentence.

The advantage to this style is that it’s not only easier to remember the rules and do correctly, but it is also more casual and conversational. This is a good thing for opens because it makes the email look less imposing, like a message from a friend.

The justification for this style is that it mimics both social media posts (none of which are done in title case) and the trend that headlines in newspapers are heading toward. Do you notice how fewer and fewer of them use title case?

Writer Owen Thomas noticed. On March 1, 2016, he reported that TechCrunch, a popular tech magazine, switched to sentence case.

When asked, editor of TechCrunch, Matthew Panzarino, said that the move was in response to news becoming more of a conversation between the publication and readers. He also noted that headlines using sentence case were often clearer. His final note was that “startup names are getting so ludicrous that it’s getting difficult to differentiate some of those headlines from Pythonesque wordplay, no matter how hard we try.”

Owens also noted in a tweet back on February 1st, 2015, that Business Insider had also switched to sentence case.

The Washington Post switched to sentence case all the way back in 2009. But publications like the New York Times have stuck to title case.

Often, it seems that headlines lead the way for subject line trends, so this slow but sure trend towards sentence case is something to watch.

Sentence case is the most conversational, so it is worth trying in less formal settings. Emails with subject lines in sentence case will seem friendly and approachable. Compare this with title case, which appears more formal.


This is the most common style used in most subject lines, especially in B2B. To do it “properly” according to MLA, AP, or Chicago style, you must capitalize these words:

  • First word
  • Verbs
  • Nouns and pronouns
  • Adjectives
  • Adverbs
  • Any word more that’s more than three letters long

Using title case for your capitalization will make your subject lines seem more polished and professional. But be warned, if your headline is too long, then using title case can be overwhelming. Try shortening the headline or switching to sentence-style capitalization.

There are also a lot of nitpicky things in title case capitalization, which resulted in some very odd capitalization in content across the web.
Owens, who I mentioned above, recommends that brands that are looking for consistency should capitalize every word in their headlines. I’d say that’s good advice for subject lines too.
Sometimes you need to seem authoritative, but you can’t do that if you are mixing up “A” being uppercase or “the” being lowercase. Perhaps it is best to just capitalize all words in your subject lines, especially with how fast content is usually released.


Technically, all three options are options for subject line capitalization can be effective in certain situations. More realistically, the decision is between sentence case and title case.

A/B testing is the only way to determine the best approach for your particular audience(s). But, to give you an idea as to where the area is trending, I searched through the first few pages of Google in 2017. I recorded which styles each blog on the topic recommended.

Here are the results:

While the sample I have here is fairly small, there are a couple of clear trends:

First, there definitely seems to be a trend toward sentence case. (And no one recommends using all caps in a subject line.)

Additionally, there were a couple blogs that showed no clear preference towards one style or another. They leave it up to the specific marketer to try A/B testing.

But what about in the inbox? Who favors what? I went through my three inboxes (two personal and a work account). These were my 2017 findings.

Out of the 17 brands included in this survey, 11.5 preferred sentence case. This seems to indicate a clear trend towards sentence-style case, something that is reflected in headlines across publications.

I decided to run a quick sample using the same brands in 2021. Most of these emails are from 2021, but a couple are from 2019. Some brands don’t email/exist anymore so the size of the list is a little smaller. Here are the results:

We see a similar set of trends from the subject lines we pulled in 2021. 8 out of 13 use sentence case primarily, 3 use title case exclusively, 1 uses all caps for the beginning then title case, and one uses all lowercase.

It makes sense, most of our private communications either only capitalize letters at the beginning of the sentence or nothing at all. It makes sense that brands would start to mimic that in hopes of better conversion rates.

There are justifications behind each style, now it’s your turn to go out and figure out what works for you. Test each style on your list and compare what works with what doesn’t.




HIPB2B is a demand gen solution provider, utilizing content, email, and marketing automation to drive outcomes for marketing and technology clients