Thanks AKI! I'm a step closer to achieving my goals. 

However, I'm getting a new error as indicated from below:

Apr 11 01:45:34 lmtp(user@mydomain.com)<20801><pVlIEJ7wrlxBUQAAUdwEFQ>: Debug: push-notification-ox: Skipped because not active (/private/vendor/vendor.dovecot/pvt/server/vendor/vendor.dovecot/http-notify METADATA not set)
Apr 11 01:45:34 lmtp(user@mydomain.com)<20801><pVlIEJ7wrlxBUQAAUdwEFQ>: Debug: push-notification: Push notification transaction completed

By the way, the file /private/vendor/vendor.dovecot/pvt/server/vendor/vendor.dovecot/http-notify does not exist on my server. 

Again, I appreciate the help :)
 
> On 11 April 2019 07:57 Robust Coding via dovecot <dovecot@dovecot.org> wrote:
> 
> 
> Hi Admin,
> 
> I hope you consider reading and addressing my concern promptly.
> 
> For the past few days I've been setting up a VPS with cPanel and WHM 
> pre-installed on Bluehost. I want to enable push notification plugin in 
> Dovecot2.3.5. I tried OX and Lua plugins and got errors.
> 
> For using OX plugin:
> push_notification_driver = ox:url=http://staging.mydomain.com/mail-notify/v1 
> user_from_metadata
> And got this error on runtime:
> Error: push-notification-ox: Skipped because unable to get attribute: Mailbox 
> attributes not enabled
> 

mail_attribute_dict = file:%h/Maildir/dovecot-attributes

> When using Lua:
> mail_plugins = $mail_plugins mail_lua notify push_notification 
> push_notification_lua
> 
> plugin {
>    push_notification_driver = lua:file=/path/to/lua/push.lua
> }
> And got this order:
> Plugin 'push_notification_lua' not found from directory /usr/lib64/dovecot
> 

You do not have push_notification_lua installed.

> I think I'm missing something here but I can't figure it out. Please HELP!
> 
> Sincerely,
> John Lopena
> 
> -- 
> 
> "Become a programmer - Lose your brain's virginity"

Aki