Undeliverable paycheck stubs

Using QB Accountants Desktop ver. 2020, when sending paycheck stubs via email - outlook.com, hotmail.com and icloud.com employee emails are getting sent back, marked undeliverable. According to our ISP, this is something to do with Microsoft and the fact that their system thinks paycheck stub attachments from QB are spam. Does anyone have a suggestion or work-around for this issue? This is from my ISP:

We heard back from Microsoft.  They agreed the server and domain reputation was not an issue.  The emails are being blocked because of content and/or formatting of the emails.

They referred us to this link 

sendersupport(dot)olc(dot)protection(dot)outlook(dot)com/pm/policies(dot)aspx

But, based on our prior experience, emails can be blocked any time they 'look suspicious'.  Some things that might be considered suspicious are:

1.     If the email includes an attachment, but not a message
2.     If there is very low contrast or invisible text - for instance white text on a white background
3.     There are misspelling in the message
4.     The message contains suspicious links -  such as if  the link or attachment address doesn’t match the sender domain