If you experience issues such as recipients using Outlook Office 365 not receiving emails from you, this is usually because some email clients have strict settings for email domains they do not recognize. So, when you use MTARGET to send emails, those using Outlook Office 365 do not receive the emails because the MTARGET email domain is not recognized. To fix this, you need to add MTARGET's domain to the whitelist.
Here are the steps to add MTARGET to the whitelist in Office 365.
Make sure you are logged in to Office 365 as an admin to add the whitelist. Then click the Admin menu.
You will be directed to the Microsoft 365 admin center page. Click the Admin Centers drop down menu, and select Exchange.
You will enter the Exchange admin center page. Select the Protection menu.
Select spam filter, then click the edit icon, then select allow lists.
In the ALLOWED DOMAIN section, click edit and add:
sp1.emailtarget.co.Click Save to save the settings.