The errors don’t really mean anything and cf7 will work for sending the forms event with the error. The main problem is not cf7 but it has to to with your sending email server and the receiving email server potentially blocking the email as spam. Setting the email other than the email of the domain will look like email spoofing. This is the problem with using anything other than SMTP to send emails. I use SMTP on several sites that still use cf7 and the errors are not an issue, I just ignore them. They really are meaningless as long the email server used for the site sends them the receiving email server does not block them. I hope that makes sense to you.
However, using SMTP means that you must use the “reply-to” address so that probably won’t help you much anyway. The place this really needs to be changed is the help desk app to use the reply to address rather than the from address.
I actually don’t use cf7 on new sites that I build and I have very few clients that still use it. It is too limiting for my clients who want to easily build their own forms as well as having both dynamic and conditional fields without needing to call me every time they want to update a form.
