If the emails are not being sent from a WordPress plugin then try first using a “from” email address that belongs to your website domain, this is the most common restriction applied in most hosting services.
If that doesn’t work please check if your hosting service requires some specific configuration to send emails from PHP/WordPress websites. The plugins use the settings specified into the WordPress website to deliver the emails, if your hosting has some specific requirements like a fixed “from” address or a custom “SMTP” server those settings must be configured into the WordPress website.
If your hosting service tells you to send the emails via a SMTP server then you can install an additional plugin to setup the SMTP configuration. You can do this with (for example) the free WP Mail SMTP plugin.