Hello,
Actually, the mentioned concern of yours specifically isn’t related to Theme end.
It could be an issue at your DNS Server end or the plugin that is being used for the Contact Forms on the Site. So, please once try contacting the Contact Form 7 plugin Support in this regard, they can guide you better.
You can also check out one of their threads in this regard: https://wordpress.org/support/topic/cf7-emails-being-sent-to-spam-2/
Further, you can check out their guide related to Setting up mail: https://contactform7.com/setting-up-mail/
Hope this helps !
Best Regards.