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While catching up on emails yesterday, I noticed that I wrote some subject lines using title case (capitalizing all “principal” words) and others using sentence case (capitalizing the first letter of the first word only).

For example, “Touching Base about Website Strategy Q2” is written in title case, also known as headline or up style. “A conference call this week?” is written in sentence case, also known as down style.

The different style guides have very different rules when it comes to capitalizing titles (here are the AP Stylebook’s and the Chicago Manual of Style’s guidelines). But there aren’t any clear-cut rules specific to email subject lines.

After some thought, I came up with three very general guidelines for subject lines for professional emails:

  1. Be sure to capitalize all proper nouns in subject lines, along with the rest of your writing.
  2. The subject line should be written in one style or the other, not a mixture of both.
  3. Be sure to capitalize at least the first letter of the first word; a subject line written in all lowercase looks less professional.

Other than these three guidelines, it’s completely up to you as to how to capitalize email subject lines.

You do not need to adopt title or sentence case for all of your emails’ subject lines; you may find one style better for some and not others. For instance, you may find that a subject line looks odd in title case—and that’s reason enough to switch to sentence case.

How do you prefer to capitalize email subject lines? Do you have any other general guidelines to add to my three? Share your thoughts!


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