A FastWebEngine email account is an email address that has a username and a password associated with it. You can send and receive email using an email account by logging in to the Webmail system and/or configuring an email client on your computer and/or mobile phone (Outlook, Entourage, Mail etc.). When you send email it will be sent from this email address, and when recipients reply to emails you send, they will reply to the email address associated with your email account.
Inbound messages >>> are delivered to >>> firstname.lastname@example.org
Outbound messages <<< are sent from <<< email@example.com
An email forwarder is not an actual email account, and does not have a username or password associated with it. An email forwarder is an email "alias" that automatically directs inbound messages to an alternate email address (or multiple addresses). You cannot send email from an email forwarder.
Inbound messages (sent to firstname.lastname@example.org) >>> are forwarded to >>> email@example.com
Outbound messages <<< are sent from <<< firstname.lastname@example.org
When you reply to messages received by a "forwarder address" they will appear as coming from the email address they are "forwarded to."
What Should I Use?
If you intend on sending and receiving email messages from a single email address — configure an email account.
If you need to have inbound messages automatically directed to another email address (or multiple addresses) — configure an email forwarder.