Mark Chayka writes in with a problem picking type for Mail in macOS:
I would like to permanently change the default font setting from “Helvetica 14pt” to “Helvetica Neue Light 14pt” in my mail application so that my messages appear as this one does.
(Trust me that his message did arrive in 14-point Helvetica Neue Light.)

You can set the default font and size for viewing and other macOS Mail elements.
I suggested he change Mail preferences: in the Mail app, choose Mail > Preferences > Fonts & Colors, click the Select button next to the Message font item (which shows the currently set font and size), and then use the Fonts selector that appears to choose your new options. (You also need to be sure that in the Composing preferences you set Message Format to Rich Text, not Plain Text, or the font choice won’t be set.)
However, Mark tried this, and while changing the Message Font did switch existing email messages’ display, it didn’t automatically use those font settings when he composed a new message. I tried the same steps on my Mac, and it worked without a hitch.
Forum posts on Apple’s site and elsewhere reveal this isn’t uncommon. Some number of people can’t make Fonts & Colors change the default composition type settings. If you have this problem and want to test whether or not it’s system-wide, you can create a new macOS account, log in, set up Mail with an email account for testing, and then see if changing Message Font works for newly composed emails. Mark tried this and had the same problem.
I consulted Apple Mail guru Joe Kissell, who has wrangled Mail for iOS and macOS as much as any human, and he was stumped as well, though he agreed the stationery feature, while clunky, would work. Reinstalling macOS might help (not a clean install, even) by knocking out some setting or kruft that’s causing this to happen. Joe has an ebook on upgrading to Sierra that can help with this.
There’s a workaround that doesn’t require system reinstallation, but which adds a few steps: use Mail’s stationery feature. (Another workaround is to pick an alternate email program!)
- Create a new email message and set the type and other options the way you want.
- Type a word both to test that the settings are correct and to leave in place in the template. (If you omit typing something, the stationery doesn’t pick up the font change.)
- Choose File > Save as Stationery.
- Name the stationery descriptively and click Save.

Creating stationery can work around a Mail bug.
Now, when you want to compose a message, you have to add a couple of steps, but you don’t have to make font menu selections:
- Create a new email message.
- Click the Show Stationery Pane button at the upper right.
- From the stationery list, scroll down to show Custom, and click it.
- Select your custom template.
- Click the word you typed, and then you can edit the message.
Stationery can only be applied to new messages, not replies.
At one point, at least one Mail plug-in would provide additional template and font features, but Apple changed the app’s architecture a few releases ago.
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