emails are disapperaing from outlook 365 for business accout immediately after being recieved

That some emails were being quarantined on your system indicated that you were being targeted, or at least being sent malware.
So it may well be that at least one of the attempts was successful, and
your system has been got-at.
With the result that the emails you are sending may be infected.
So the recipients systems are quarantining them, or just deleted if that is what their system is set to do.
Or their ISP is detecting the inappropriate content and either putting them in the ISP (IMAP) Spam, or Junk folder (probably with a 30 day retention before they get deleted, or just deleting them as it finds them.
That the emails shows for a short period in their emails indicates their PC has some anti-malware processing set - maybe whatever they have installed to help protect their system, or built-in actions associated with Windows security, or Outlook settings.
I would start by using a browser based app to view your emails and see if that shows the wanted emails, or some are missing.
Then, maybe doing a full scan with your protection app,
As well as asking those with missing emails to check if their, or their ISP's systems are finding malware, or what MS deem "UNSAFE" content.
If you have a "Sig" block it may be that there is something in that.
and, from experience ISP checking may be identifying innocuous entries as malware, or -
for those not getting the email at all, you or your ISP may have been blacklisted as a (now known) malware source.