I found the problem.
It is not with any other plugins, but with WP’s core.
I am not much of a coder, but I just started my WP site, and only have a few plugins active. None of them other than Contact Form 7 use email.
Any emails that I sent using the Contact Form came across with the SMTP From address of mine, and the SMTP Reply address as the one filled out in the form.
I found this setting:
Settings > General
There is a setting for Email Address that states:
“This address is used for admin purposes, like new user notification.”
I blanked it out and the emails from the Contact Form 7 started coming across correctly, the SMTP From and SMTP To address’ were the same.
Previously my SPAM filter had been blocking the emails as it looked like someone was spoofing my email address, but after the change they are now coming through just fine.
Now, if someone could figure out why this email setting is overriding the outbound email from the Contact Form plugin, and fix it…