Hello,

1. You can place the email address in the username field. (example: test@mail.com)
2. Sorry, post only can be sent by one email address (specified in the username field) but multiple email accounts can send email to specified username to be posted to the blog.
3. Sender whitelist is to tell easyblog only fetch an email from this list. Only applicable if the field is not empty. If the field is empty, Easyblog will fetch any email from any account. Map email to the user's email is used to only fetch email if the email address is also belong to any blogger in the site.
4. Select a user is for the author of the blog post. Every email fetched from the inbox will be assigned this user as an author of the blog post. http://screencast.com/t/HrNd3IxoQtr

Hope this helps.