Connect PowerShell to 365 Then use these commands to block senders:
#Add Sender Block
$Email = “email@domain.com”
New-TenantAllowBlockListItems -block -ListType Sender -Entries $Email -NoExpiration
#Remove Sender Block
Remove-TenantAllowBlockListItems -ListType Sender -Entries $Email
#Get Block Summary
get-TenantAllowBlockListItems -ListType Sender |select value,action
#URL Block
$URL = “domain.com”
New-TenantAllowBlockListItems -ListType Url -Block -Entries $url -NoExpiration
#SPAM FILTER RULES
Get-HostedContentFilterPolicy
#HELP
get-help New-TenantAllowBlockListItems -online