We are getting confirmation message as email sent, but email not being sent or not reached to mail box?

For some of the ISP (hosting providers) have restriction to have only dimain email IDs are accepted to send the email for some security concerns. So if you are using Third Party like Gmail address it might get blocked by the SMTP server but you would not get the error on the interface. In some cases there would be domain specific, so try with different email addresses.

It is problem with the host stopping the email. One of the main reason could be length of the email, it is should be having a minimum length, others would be email stopped by the host. Please tryhttps://wordpress.org/plugins/wp-mail-smtp/