You can make Airmail as the default mail client for your OS X device.

Approach 2 To Set Outlook as Default Email Client in Mac OS X. If end users have Outlook 2011 for Mac on their local system, then, users can set it as the default from there. This same procedure will be applied for Outlook 2016 automatically. Approach 3 To Set Mac MS Outlook 2016 as a Default Email Client. Additionally, users can use IC-Switch. Apr 12, 2018  Instead of launching the default macOS Finder, “Open in Finder” or “Reveal in Finder” commands will launch Path Finder. Whenever you download an application that replicates a system functionality, look for a way to set the downloaded application as the default. You’re likely to find it.

To make Airmail your default mail client go to Apple Mail app preferences and set default mail reader as Airmail as shown below.

• Make Outlook (Office 2016) the default email app on Mac OS 10.11 - El Capitan I just installed El Capitan as well as Office 2016 on my Mac and am wondering how do I make Outlook the default email app? This thread is locked. You can follow the question or vote as helpful, but you cannot reply to this thread.
• Jun 23, 2020  Apple's iOS 14 Preview page mentions in the Settings section, “Set a default web browser and email app that launch when you click a link or want to compose a new mail message.”.
• The Mail default setting is in the Mail app Preferences panel under “General” as described in detail in this article. From the Mail app you set Mail or Thunderbird or any other email app as your default email app on Mac. You should read it before commenting.

If the above process does not work, please follow the steps:
You can reset Apple's Preferences Database.
Open Terminal (Cmd+Space Bar and enter Terminal)
Copy/paste/enter this command:
/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -all local,system,user
Then set the default preference in Apple Mail again.

Published on: 01 / 11 / 2019

This article explains how you can set different applications to open PDF files on your Mac. Your Mac has a built-in PDF reader to open and render all of your PDFs on your Mac. This default application is called Preview. Following the instructions below, you can easily set your preferred application (such as Adobe Acrobat Reader) as the default application for opening PDF files. If you are unhappy with the results, again using the instructions below, then you may set the default PDF viewer in macOS back to Preview.

See also: Preview: The File Couldn’t Be Opened, Fix

Sometimes, Mac users accidentally make other applications as the default PDF reader and want to restore Preview as the default. Sometimes, Mac updates may cause issues with the default PDF reader. This article may help you resolve these issues.

See also: Can’t Open PDF On iPhone Or iPad, Fix

Setting your preferred app as the default PDF reader in macOS

For this article, we will set Preview as the default. Here is how:

1. Select any PDF file on your Mac.

2. Right-click (or Control-Click) the document. This will reveal a menu.

3. Select Get Info. This will a new window: (You can also open this info window by selecting the document and clicking the Command I keys.)

Default Macos Font

4. Find the Open With section. If the section is closed, click on the arrow next to it to expand.

Macos Defaults Command

5. You will see a pull-down menu. Open the menu and find and select Preview. (If your preferred app is not in the list, choose Other. This will let you choose your app from your applications.)

Macos Change Default Email App

6. Once you select your application, such as Preview, click the “Change All” button to have this application to open all PDF documents.

7. A popup will appear saying “Are you sure you want to change all similar documents to open with the application “Preview”? This change will apply to all documents with extension “.pdf”. Click the blue Continue button to confirm.

And you are done.

See also: PDF Won’t Open: “Please Wait…” Message, How To Open