First, ensure that the web.config files for both (Net & AsiScheduler) are set identically under the <mailsettings> section on both web.config files using the correct O365 Account info. Please, reference to this other public knowledge base article for more details when configuring your smtp settings for iMIS Communication Suite using O365. Click here.
If iMIS Communication Suite is displaying the message was sent and delivered, then that typically entails the email was relayed out through the smtp protocol (internet), and it should have gone out sucessfully.
There may be other subtle concerns with the emails once they are in transit in the internet to the recipients' mail server. Often times messages could have potentially be caught as false positive. Please, reference to the followig Microsoft Articles.
A "false positive" is a legitimate email message that was incorrectly identified as spam. Because of the high volume of submissions that we receive, we may not be able to answer all requests for analysis. Admins can send email, url, and attachments to Microsoft for review. See Admin submissions in Office 365 ATP
Other example, it could be related to the actual messages being force to the junk folder in the recipient's mail client such as (outlook, gmail, etc).
Similarly, important is to ensure adding the iMIS App server's IP address to the allow list in your O365 (Admin - Exchange) portal: