Website Membership Plugin + mail server authentication
We don't currently support mail authentication as most hosting companies "white-list" emails that come from their own servers.
We have had a couple people ask about it lately, though, so it's on the list for v2.52. So if you like you could help us beta test it.
If you're not on the beta list already just email me at email@example.com and I can add you.
Hope that helps!
Unfortunately, white listing is not an option. My hosting company's policy has changed and they no longer permit unauthenticated mail sent for any account.
That's great news about this feature being built into v2.52. I am on the beta test list and will be sure to check that out.