Maybe you should clarify your definition of 'viewing'. Resting your eyeballs on a record is not enough ...
But kidding aside: if the record with the desired mail address is the *current* record, then that should work as you intend, i.e. the mail address should be pulled from that record.
If all else fails, show us your script and tell us how it is triggered.
Often, the way to do this is to put a button in the right spot. A button placed in the body of a list view or in the row of a portal means that a mouse click on the button puts the focus on the layout record (list view) or related record (portal) first then performs the script starting from the context of that focus.
In Filemaker 13, I use a template that has a Button with a picture of an email. (It says it's a button in layout). The button is next to the email address field I have for a database of members in a club I belong to. This button is set to run a script that's called "send email" which, when I go Scripts>Manage Scripts, looks like this. Cut and paste as you wish. When you want to send an email to only 1 record, I click on this button rather than use the File>Send>Mail pathway. It sends an email to whatever address is in the field named " Email 1 "
Hope it helps. I'm no FM guru by any stretch.
I think Phil has the answer I need.