Incoming SPAM Email from Gmail

hemen1645 

Since this is Gmail user, you may file a abuse report directly to Google , so they could investigate the account and they will find with similar behavior, pattern, IP and other methods to block user:

https://support.google.com/mail/contact/abuse 

Meanwhile, ask your users to mark this as Junk, so Anti-Spam algorithm in Microsoft Outlook could identify spam pattern and learn to block it.

You may use admin submission in Microsoft 365 portal and submit some sample of it:

https://docs.microsoft.com/en-us/microsoft-365/security/office-365-security/admin-submission?view=o365-worldwide 

You will find some useful resources here:

https://docs.microsoft.com/en-us/microsoft-365/security/office-365-security/anti-spam-protection?view=o365-worldwide

hemen1645 Hello, I assume that your spam filter policy is adjusted in a way that suit your needs? We've changed a few default settings and are using the more strict recommendations from Microsoft (most of it ends up in quarantine). Still there is no way to be 100 % as our users do get spam and phishing sometimes. Anyway, as a consequence we enabled the tool "Report Message" about a year ago to the entire organization and now our end-users are managing the occasional spam/phishing from within their own clients. It's a great tool for reporting messages to Microsoft and user friendly as well. Perhaps not applicable for your org/scenario but I just wanted to share my experience.

hemen1645 

This is a tricky one as you cannot block gmail.com (well you can, but that is not a practical solution).  Are there any other common factors in the emails that you are receiving (such as the subject for example)?