It's got to do with your server's mailing settings, have you tried using SMTP with like a WP SMTP plugin, improves eMail deliverability.
Edit: You can even do another plugin that logs all eMails going out from your server so you kind of can keep an eye there, there are even plugins that let you resend emails from those logs if you feel like it wasn't sent or if there is an error while sending it.
Probably!? Google "How to smtp gmail wordpress"do you mean what plugin?
what is the Easy WP SMTP plugin?
can the plugin solve my problem?