[Rehan]

I can't stress this enough but when requesting for help and support try to provide as much information as possible.

1. Is your Wordpress site hosted on shared hosting or your own server?
2. Which web server, PHP and MySQL or MySQL derivatives versions are used?
3. If shared hosting is used: are you allowed to send mails? Some providers disable this function due to spam.
4. If you use your own server: is a local MTA installed to send mails or do you use a 3rd party service such as Sendgrid or similar?
5. Are you running the latest Wordpress and using the latest version of the plugin? A link to the actual used plugin would be helpful, too.

If you run your own server have you checked logs in /var/log?

Have you tried debugging this issue before by yourself? What were the results? Have you discovered something?


Little side question: How come you always post this kind of threads in the wrong forums?

OFF: For me it was in correct section.As i were asking about the function wp_mail() and off-course that is about scripts.

ON
I have hosted site on my own server
I am using Apache2, PHP 7.2, MySQL Version  5.7.26
I don't use any MTA.
Yea i have latest version of wordpress.
Here is the link to the plugin https://wordpress.org/plugins/contact-form-7/

BTW i have installed a WPForm SMTP.Now it is working well.But i am still interested to know why was it not working before and how to fix this manually because the email system is working well with this plugin using gmail.but i still need to fix that because the subscribe plugin is not able to send mails.
I have not decided any plugin yet for subscription.suggest me a if you have information about them.

https://wordpress.org/plugins/email-subscribers/
https://wordpress.org/plugins/mailchimp-for-wp/