On Bluehost, using S2Member, can't change from email address

Hello. Been struggling with this for a couple of weeks (off and on).

I am hosting with Bluehost. Client has an exchange server for email – MX record points to that. Web address points to Bluehost (nameserver is at network solutions).

We have a site running s2Member Pro and everything is fine except that when a user registers the from email address has a [email protected] email address.

If I change the from address with a mail_from plug in, and with a php.ini edit, this works to change the from address, but then some email providers are not delivering the registration emails. There is an email account setup on the server that matches the from email address (the from email address is one that is currently being used on the exchange server, BTW).

So my next action to try to get this to work was to install a SMTP plugin, and when that is configured and tested all I get from any SMTP account I set up is a connection failure.

My guess is that the email is failing (to some recipients) because the email is not being trusted. Not sure why the SMTP is failing. Working on that. But looking for other thoughts from people. Anything I can change, remove from DNS records on blue host?

Is there a way to at least set a reply to address, even if we have to stick with the boxXXXbluehost.com email address?

Thanks