that MTA-STS records apply only to SMTP traffic between mail servers while communications between a user's client and the mail server are protected by Transport Layer Security with SMTP/MSA, IMAP, POP3, or HTTPS in combination with an organizational or technical policy. Essentially, MTA-STS is a means to extend such a policy to third parties. In April 2019 Google Mail announced support for MTA-STS. SMTP TLS Reporting Protocols designed to securely deliver messages can fail due to misconfigurations or deliberate active interference, leading to undelivered messages or delivery over unencrypted or unauthenticated channels. "SMTP TLS Reporting" describes a reporting mechanism and format for sharing statistics and specific information about potential failures with recipient domains. Recipient domains can then use this information to both detect potential attacks and diagnose unintentional misconfigurations. In April 2019 Google Mail announced support for SMTP TLS Reporting. Spoofing and spamming The original design of SMTP had no facility to authenticate senders, or check that servers were authorized to send on their behalf, with the result that email spoofing is possible, and commonly used in email spam and phishing. Occasional proposals are made to modify SMTP extensively or replace it completely. One example of this is Internet Mail 2000, but neither it, nor any other has made much headway in the face of the network effect of the huge installed base of classic SMTP. Instead, mail servers now use a range of techniques, such as stricter enforcement of standards such as , DomainKeys Identified Mail, Sender Policy Framework and DMARC, DNSBLs and greylisting to reject or quarantine suspicious emails. Implementations Related requests for comments – Requirements for Internet Hosts—Application and Support (STD 3) – SMTP Service Extension for Message Size Declaration (оbsoletes: ) – Anti-Spam Recommendations for SMTP MTAs (BCP 30) – Simple Mail Transfer Protocol – SMTP Service Extension for Command Pipelining (STD 60) – SMTP Service Extensions for Transmission of Large and Binary MIME Messages – SMTP Service Extension for Secure SMTP over Transport Layer Security (obsoletes ) – SMTP Service Extension for Delivery Status Notifications (obsoletes ) – Enhanced Status Codes for SMTP (obsoletes , updated by ) – An Extensible Message Format for Delivery Status Notifications (obsoletes ) – Message Disposition Notification (updates ) – Recommendations for Automatic Responses to Electronic Mail – SMTP Operational Experience in Mixed IPv4/v6 Environments – Overview and Framework for Internationalized Email (updated by ) – SMTP Service Extension