PowerShell script to add work email to the list fields for the author

The Author (Created By) field is actually an lookup field to the hidden User Information list.

If you need to add the work email of the Author (Created By field) user to a specific list it can be done by adding a dependent lookup field for the Author field:

$site = get-spsite "site url here";
$list = $site.RootWeb.Lists["list name"];

$createdByEmailGuid = $web.Fields.AddDependentLookup("Work e-mail", [Microsoft.SharePoint.SPBuiltInFieldId]::Author);
$createdByEmail = $web.Fields.GetFieldByInternalName($createdByEmailGuid);
$createdByEmail.Description = "Work e-mail address of the Author.";
$createdByEmail.LookupField = $web.Fields[[Microsoft.SharePoint.SPBuiltInFieldId]::EMail].InternalName;
$createdByEmail.Update();
$web.Update();

$list.Fields.Add($createdByEmail);
$list.Update();

If additional fields are needed the same method can be applied. Here is a list of fields that can be added from the User Information list:

- Work e-mail
- Mobile phone
- About me
- Picture
- Department
- Title
- SIP Address
- First name
- Last name
- Work phone
- User name
- Web site
- Ask Me About
- Office