Updated en_US.yml translation file and prevent appending of Reply-To addresses when iterating through multiple recipients

...f SendEmailFromField (Used for 'Reply To' not 'From')

Updated en_US.yml translation file to more accurately reflect function
of SendEmailFromField (Used for 'Reply To' not 'From').  en.yml seems
to be correct. Also updated REPLYADDRESS to be more consistent
(capitalisation).

Also, when there are multiple recipients and each recipient has a Reply-To
email address (either explicitly specified or taken from email form
field), as the script iterates through the list of recipients to send
emails, the Reply-To addresses get appended for each successive
recipient.