With this accomplished you can write your email, then when you're ready to send it select Options > More Options > Message Options > Security Settings > Encrypt message contents and attachments.
Sadly these features are not available on Outlook.com or in the Mail app for Windows 10, as they are restricted to paid subscribers.
What if I don't use Gmail or Outlook?
There are a number of decent alternatives out there, with Tutanota, Ghostmail, and Protonmail all proving excellent options. At the moment you can have free accounts on these, although they do come with restrictions on usage in regards to the size of emails you can send and the storage available.
Secure services either require the recipient to also be a member of the platform, or to possess a password you give them to unlock each email. This might seem cumbersome when compared to the likes of Gmail, but is a necessary level of security that is very effective against hackers and government agencies.
If you're happy to use an IM style of communication then Mega offer a secure chat feature as part of its free cloud storage package. Again your recipient would need to be a member, but as it doesn't cost anything and also affords you 50GB of storage, this might actually be quite enticing.
See also: Best online storage services
How do I send messages that self-destruct?
Another method is to use software that deletes the messages shortly after they've been read. As an example for how one of these secure message service works we signed up to Snapmail, which allows users to send 'self-destructing text emails for Gmail'. It all feels very James Bond, but is actually quite easy to get to grips with and involves almost no international villainy.
The first thing to do, assuming of course you use Gmail, is to visit the Chrome web store and search for Snapmail. When you've found it click the Add to Chrome button and the extension will be installed.
Now click the three lines in the top right of the screen and from the drop down menu that appear select More tools>Extensions, then scroll down until you find Snapmail and ensure that it is enabled.
To send an encrypted email you'll need to launch Gmail, compose your message, then you'll notice that there is now a Snapmail next to the Send button at the bottom of the window. This means you can choose to only encrypt certain emails rather than every one, but remember that any sent by Snapmail will automatically be deleted. Click the Snapmail button to encrypt your message.
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