You can save a copy of an individual email to your system in two file formats:
HTML
EML
To save an email:
Click the More options icon at the top-right corner of the email detail view.
Select Save as from the menu list.
Choose either HTML or EML file format.

Notes:
The file will be saved to your configured download location.
To save all emails in a threaded conversation, you must download each thread individually. Downloading the parent thread alone will not include its replies.
Emails can be saved in HTML format even when offline. To save emails in EML format, you need an internet connection.