Newton saves the email you're writing as a draft, so you can finish it later. Drafts are saved to your email account, so you'll find them on your other devices too.
Steps
Desktop
Close the compose window. If it asks Save draft?, click Save. Newton also saves a couple of seconds after you stop typing.
To pick it up again, open Drafts in the sidebar, or press G then D. A draft reply also shows in its conversation: hover over it and click the pencil (Edit draft).
To delete the draft you're writing, click the trash button (Discard draft) at the bottom of the compose window, then Discard.
iPhone, iPad & Android
Tap × at the top left of the compose screen, then Save Draft. Newton also saves when you switch to another app.
To pick it up again, open Drafts from the menu. A draft reply also shows in its conversation, with Edit and Send Now.
To delete a draft, tap × and Discard while you're writing it, or tap ••• on the draft in its conversation and tap Delete.
Good to know
Gmail and Outlook drafts are kept in your account's Drafts folder, so Gmail and Outlook on the web show them too.
For IMAP accounts such as iCloud or Yahoo, drafts you write on desktop go to the account's Drafts folder, but drafts you write on your phone stay on that phone.
Reply or Reply all reopens a draft you already started in that conversation, unless someone has replied since.
Send Now on a draft card sends it straight away, without the undo delay.