Had this exact issue when pushing emails through Office 365. This hack gets it working in vb5 5.4.5, but does not have the Reply-to because I didn't want to mess with figuring that out. So it sends and receives as the same user that you define, but the message body still has the user's email address .
In this file: ./core/vb/api/contactus.php
Replace:
PHP Code:
$flood = vB_Mail::vbmail($destemail, $mailcontent['subject'], $mailcontent['message'], true, $maildata['email']);
With:
PHP Code:
$flood = vB_Mail::vbmail($destemail, $mailcontent['subject'], $mailcontent['message'], true, $destemail);