Updated Tue 10 May 2016
Gravity Forms doesn’t return or record success or failure of emails, so you may find yourself having to resend them if there was a problem.
It is already possible to trigger notifications for form entries again via the WordPress admin interface, but it requires a lot of clicking should there be very many of them. Also, although the Directory Columns option allows you to customise the fields displayed, the entry submission date/timestamp is not available here.
You can also view a summary of the main notification settings (from/to/reply-to addresses, subject line) for all (or selected) forms.
Full syntax/help is available with:
wp help gftuil renotify wp help gfutil notifications