Dear CF7 Support Team,
The "From" attribute of CF7 Mail(2), whether used natively, or alongside WP-Mail-SMTP, is broken. Disabling WP-Mail-SMTP (and thus returning to the native WordPress mail functions) does not resolve the issue. However, using WP-Mail-SMTP to override whatever "From" value is input in outgoing e-mails, does resolve the issue.
That said, the issue only seems to present itself when the web hosting and e-mail functions of a domain are performed on different networks. And while I considered that this might be a problem with the web host of choice, WP-Mail-SMTP proves otherwise. Please let me know if you have any additional questions.
S. Wyatt Young