On the Mac, you can email a PDF of almost any webpage, photo, or other document, by selecting the print command and picking “Mail PDF” from the dropdown menu at the bottom of the dialog box that pops up. This automatically opens Apple Mail, regardless of what you’ve set as the default mail client on your Mac. What if you want to mail the PDF using a third party mail client?
A post over in the MacRumors forum had the answer. You need to place an alias to your email client of choice in the /Library/PDF Services/ folder on your Mac.
Create an alias by right-clicking (or Control-clicking) on the email app of your choosing, and choosing “Make Alias.”
You can rename the alias to a name of your choosing (such as “Mail PDF with Airmail”). Then move the alias to the /Library/PDF Services/ folder on your Mac. This is the library folder you can get to by holding down the Option key on your keyboard, while selecting the “Go” menu in the Finder menubar. That will cause the Library folder to appear.
Once you’ve moved your alias to the PDF Services folder, it should show up in your PDF dropdown menu.
I’ve tried this with MailMate and Airmail, and it works fine. I haven’t tried with other types of apps that accept PDF content to see if it works there, too.