MSpina59 wrote:

There isn't really a reason code wise for some emails in CB to work and not that one as they all use the same API to send emails.

It looks like this sentence is not 100% true, at the end.
In fact using one of the two possible choices of the "Emails sent from" parameter the form doesn't work.
Many thanks again for your time.

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Thanks for confirming that you could make mail work for your environment and not land in spamboxes, by using the setting "send from admin mail, with reply-to to user mail" (if that assumption is not correct, please reply).

The mails are indeed sent with both settings, just the deliverability is much better with the admin email address sending because of SPF and as consequence DMARC. The description of the parameter explains well the advantages and disadvantages of each setting, and there are numerous articles on the Internet about the subject.

So, marking this thread as solved, and opening separately a Feature Request to try to better address the initial setting hassle you had:
forge.joomlapolis.com/issues/8539