Hi, that is something already seen. When you send an email with a client it is delivered, when send with a hoster mailing system it is not. Probably some providers do no accept emails from IP of specific hosters or not whitelisted.
That is not connected to the plugin, it just create an email, it’s the mailing system of the provider. I can suggest to try with a pro delivery service, like amazon, sendgrid, …, smtp2go, …, or ask the provider if you can use their smtp.