Hi,
I am writing to you to let you know your developers are not complete noobs. They have set the settings properly but the email sending is something which can't be controlled by just code.
See when email leaves php script it goes to the google SMTP server. After that it is relayed to recipient mailbox through spam filters and not what.
So, I ask you :
1) is email sending completely not working form address 2?
2) have you checked the sent items folder of address 2 googe account. I mean if the email has made up to the google SMTP, then it will be available in sent items folder.
3) PM me :)