Lots of MX domains has implemented Sender Policy Framework (SPF). SPF is a simple email validation system designed to detect email spoofing by providing a mechanism to allow receiving mail exchangers to check that incoming mail from a domain is being sent from a host authorized by that domain's administrators. The list of authorized sending hosts for a domain is published in the Domain Name System (DNS) records for that domain in the form of a specially formatted TXT record. Email spam and phishing often use forged sender addresses, so publishing and checking SPF records can be considered anti-spam techniques. Sender Policy Framework is defined in IETF publication RFC 7208 Liquid Files is not compliant with SPF. For example : If an external user send a secure message to internal user. He will reveive back a confirmation e-mail sent from liquidfiles with his own address as sender. Liquid Files system spoof his domain name. E-mails sent from liquid files to external users should be ONLY sent with internal users e-mail or admin e-mail.