In places where you can enter an email address for notifications of various types, FreePBX does not allow entering multiple email addresses separated by a comma nor does it allow addresses ending in @localhost. This means users have to resort to ugly hacks like the one detailed at http://pbxinaflash.com/community/index.php?threads/how-to-send-voicemail-to-email-to-multiple-email-addresses-and-pager-addresses.14012/ in order to send emails to multiple addresses, or in the alternative, use a program like phpMyAdmin to insert the actual desired value into the database.
IMHO the PBX software should not be enforcing restrictions on what is placed in an e-mail field, but if it is felt that is necessary for some reason then it should at least allow for these common scenarios. An easy fix would be to simply remove any error or validity checking on these fields, and an only slightly more difficult one would be to simply allow @localhost and comma-separated email addresses in these fields. This affects not only voicemail and dictation services, but also system upgrade notifications.