Test emails are sent, but when i try to send from contact's page i get an error

Your software
My Mautic version is: 4.1.2
My PHP version is: 7.4.27
My Database type and version is:

Version 10.3.31-MariaDB-0+deb10u1
Doctrine driver pdo_mysql
Doctrine database platform (automatically detected) Doctrine\DBAL\Platforms\MariaDb1027Platform

Your problem
My problem is:

I configured my Email SMTP (I’m suing Kirim’s transactional SMTP relay) and succesfully send and receive the test email.

Then i created a contact and tried to send an email from the contact’s page and i get an error.

These errors are showing in the log:
Failed to send to ds@myemaildomain.co: Expected response code 250 but got code “550”, with message "550 Message denied "

Steps I have tried to fix the problem:

Reviewed the Email settings, tried TLS 587 (connection and email tests are successful) and SSL 465 (connection and email tests are successful) both fail after i try to send from contact’s page with the same error.

I’m a 100% newbie, this is my first go at Mautic, so all the help is highly appreciated!

TIA!

Hello!
Message denied means your email left your smtp but the recipient doesn’t want to recieve it.