@John - thank you for helping out and sharing your experience.
@pdirect - I ran some diagnostic tools on your account. I think John is onto something with the verified emails. The emails may be verified for their own sender, but they may not be verified for sending through each other. Let me explain....
Your general settings seem to be AT&T (this is under Customize > My Account). However, one user (we'll call "ej" for security purposes) had personalized settings for Office 360.
AT&T (general settings under Customize > My Account)
On your general account settings the tools could only get it to send using port 25, SSL turned OFF. It looks like that account doesn’t actually support SSL/TSL, as when either port 465 or port 587 are specified, yahoo comes back with a timeout, or explicitly says the account doesn't support SSL.
Even with these settings, it would only work if the from email address (sender) was coming from a known, and validated account name, p******t@s**g***.net (* are for your security, as I'm sure you can fill it in). If other email addresses were used as the from account name, it gave an error “"Mailbox name not allowed. The server response was: From address not verified - see http://help.yahoo.com/l/us/yahoo/mail/original/manage/sendfrom-07.html"”.
This is not on our end, it is yahoo not recognizing the sender email address as someone who is allowed to send through the p******t@s**g***.net account, and blocking the send. So, it looks like all potential senders (which are all user email addresses) need to be listed with yahoo or att. That web link takes you nowhere…yahoo needs to update their articles and links.
Office 360 (user specific settings under Customize > Users)
On the personal settings for user "ej" under Customize > Users, the account you are using is email server username b***@p*********.com. Here the diagnostic tools send successfully with port 587, SSL turned ON. But same deal, emails must come from a sender that is registered with them, otherwise Office 360 comes back with "Mailbox unavailable. The server response was: 5.7.1 Client does not have permissions to send as this sender". The personal settings for "ej" is a different email from b***@p*********.com, and not one that Office 360 recognizes as a valid sender from the b***@p*********.com account. However, if emails are sent from b***@p*********.com (by temporarily changing the email address for "ej" to b***@p*********.com, then life is good.
My recommendations:
OPTION 1 (best): have each user have their own Office 360 account setup under Customize > Users and to make sure that the account owner matches the email address each time. i.e. for "ej" use ej's Office 360 email account instead of yours.
OPTION 2 (2nd best): modify the
b***@p*********.com email account to allow the other users to send from that account (you need to do that directly with Office 360).
OPTION 3 (worst option, history says that AT&T/Yahoo will continue to be problematic): If, however, you want to stick with AT&T, I would recommend that you modify the account to support SSL, and find out from them what the preferred port is, and also to make sure that ALL users' email addresses are registered to send through the
p******t@s**g***.net account.
HTHs,
Paul