Whether you are writing a new email, or replying to or forwarding an existing email the Write Message page is the same.
Action Bar
You will notice the Action Bar changes and provides you with these options:
Message Header
The message header is where you set the address information for your message. The following options are available:
HTML Formatted Email
To send HTML formatted email, select the the HTML option in the lower right hand corner of the Write Message page.
Attachments
Attachments are limited to 20mb. If you need to send an email with attachments larger than 20mb, please consider using a compression program like 7zip.