You may want to restrict users from uploading attachments of certain sizes, or block users from uploading any attachments in Dynamics 365. Here we will go through how to configure this.
Under System Settings, go to the Email tab. Here you will see Set file size limit for attachments, Maximum file size (in kilobytes):
Set this to 0 and click OK:
Now when a user tries to upload an attachment, they will see the error below:
This error is the same as if you configured the maximum size to be say 5120 and the user upload a 6000 size file.