I was not able to find a solution for entering a password into my mac mail via something like last pass. I think that you will have to use the paid version of something like https://protonmail.com
. The non-paid version has to be used through a browser, which opens you up to hacking you password on the endpoints for a brief period until you get logged in. The paid version actually installs software on your local host that will handle the encryption of your password via your email applications such as outlook or the mac mail.
Please visit their site to get the most accurate information on this, but this is my understanding of how their software works. Please keep in mind that I haven't tried this myself and it has been some time since I last looked at it.
I hope this helps.