An email can be downloaded as an .eml file. This allows you to open the file in your chosen email service and reply-to or forward this email.
To download an email, click the download icon in the top-right corner of its tile.
Email attachments can also be downloaded. Only top level archive files (i.e. zip) are supported. That is you will need to download the whole zip and extract the file, if the file they are looking for is inside.
To download an attachment, open the desired email, hover over the attachment and click the download icon next to the attachment.