Updated Mailspring to 1.7.8 which includes critical fixes for users on SMTP connections and Office365 linked Outlook Accounts.

Changelog:

• Resolves a critical SMTP connection problem on Linux for Office365, manually configured Gmail, and other accounts that used the LOGIN SMTP authentication mechanism.
• Plain text messages using a multipart MIME structure with one or more attachments now render correctly as plaintext.
• "Sync Mail Now" is displayed in Preferences > Shortcuts so it's easier to map it to a custom shortcut.

Tested 1.7.8 by sending, recieving, and archiving emails from a Gmail account. Everything functioned and looked as expected.