When sending emails from Apple mail with attachments or perhaps just Mac an additional attachment ” nameless.htm” gets added as an attachment.
In Microsoft 365 , if you have your malware filter enabled and .htm , .html in the list of attachments to block, legitimate emails will get blocked.
we resolved the issue as follows.
1. Do not add .htm & html to the list of files in malware filter.
2. Create a transport rule as shown below.
Works like a charm