That's what they say in their T&C and sample this https://help.zoho.com/portal/en/community/topic/unable-to-send-message-reason-554-5-1-8-email-outgoing-blocked

That's what they say in their T&C and sample this https://help.zoho.com/portal/en/community/topic/unable-to-send-message-reason-554-5-1-8-email-outgoing-blocked-18-1-2019 https://help.zoho.com/portal/en/community/topic/unable-to-se... Then actually went to a reddit post and repeated the same things there.