Hi,
To change the replyTo address you just have to set it on the settings interface, by default it does not show yo, you have to click on the link right below the email body to add it.
There's some issues and confusions though that I'd like to explain regarding the reply address.
Basically, a email header has many address, e.g. the "from" address, the "reply to" address and recipients addresses, including "To" and "Cc" ("Bcc" is normally empty, since that's the whole point of it, but Gmail now has a feature that shows yourself on the emails "bcc" if you received an email from gmail because you were on the "Bcc" list).
The decision of what will happen when a user clicks the "reply" button, really depends on their email client (e.g. outlook, firebird, or web clients as hotmail and gmail). Normally, if the "reply to" field is filled, they use it automatically as the recipient of the reply, but that's not a universal rule.
Gmail for instance have an issue with the reply to. If the "From" address is either the same as the "To" address, or is configured in Gmail Settings as one of your 'Send As...' accounts, Gmail replies to the "To" address instead of the "Reply-To", and that's just how Gmail works. You can see some discussions here:
http://stackoverflow.com/questions/2421234/gmail-appearing-to-ignore-reply-tohttp://www.google.com/support/forum/p/gmail/thread?tid=74d00d5e2605242d&hl=en
So, in order to check if your FormEmailer replyTo setting is working good, don't send the email to your own gmail or any of your "send as" accounts.
Now, most people really want to change the "from" address, not the "replyTo". But the "from" address is not a configurable field, which is expected, since we
don't want people sending email on behalf of others (although that
happens a lot with spammers).
The "from" address is always the primary address of the account running the script (not the spreadsheet or script owner).
When you're processing it manually (e.g. via the menu), it's the account of who's clicking the menu.
When it's running automatically via a trigger, it's the account of who set up the trigger in the first place.
So, to change the "from" address, you have to log in with the original account and remove the trigger you've set using it.
Then log in with the desired account and set the trigger again.
Hope that clear things.
Henrique G. Abreu