E mail service is not working using Local host instead of smtp server

Hello support team, we have recently upgraded to OJS Our hosting provider says to use local host instead of SMTP for sending emails. These are the settings:
Use SMTP for sending mail instead of mail()
smtp = On

; SMTP server settings
smtp_server = localhost
smtp_port = 26

Enable SMTP authentication
Supported smtp_auth: ssl, tls (see PHPMailer SMTPSecure)
smtp_auth = none
smtp_username = ******@jmedsci.com
smtp_password = ******

Supported smtp_authtype: RAM-MD5, LOGIN, PLAIN, XOAUTH2 (see PHPMailer AuthType)
; (Leave blank to try them in that order)
; smtp_authtype =

; The following are required for smtp_authtype = XOAUTH2 (e.g. GMail OAuth)
; (See Using Gmail with XOAUTH2 · PHPMailer/PHPMailer Wiki · GitHub)
; smtp_oauth_provider = Google
; smtp_oauth_email =
; smtp_oauth_clientid =
; smtp_oauth_clientsecret =
; smtp_oauth_refreshtoken =

; Enable suppressing verification of SMTP certificate in PHPMailer
; Note: this is not recommended per PHPMailer documentation
; smtp_suppress_cert_check = On

However only the system admin can send email via OJS all other users including Journal manager, editors and reviewers are unable to send email. The OJS generate the following error:
SMTP Error: data not accepted.SMTP server error: DATA command failed Detail: Relaying not allowed
SMTP code: 530

Kindly help me in fixing this issue

To use localhost instead of smtp for sending mail, change the smtp setting to “Off”.

I did smtp:off . The problem still exists, the error this time;
Could not instantiate mail function.

This means that PHP is configured to disable the built-in mail() function. You’ll need to clarify with your hosting provider what they mean by “use local host instead of SMTP for sending emails”.

Your local host, if PHP has the mail() function enabled, can send email without an initial SMTP connection.

Your local host may also accept an SMTP connection (which was the first configuration you shared). However, the error message “Relaying not allowed” indicates that your local SMTP server needs to be reconfigured to allow local SMTP connections, or that your local SMTP server requires authentication.

Your hosting provider will need to direct you on what the expected configuration is.