Editing Simple Mail Transfer Protocol (section)

==Spoofing and spamming==
{{Main|Anti-spam techniques|Email authentication}}
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 {{IETF RFC|5322}},<ref>{{cite web| url = https://support.google.com/mail/?p=RfcMessageNonCompliant| title = Message Non Compliant with RFC 5322| access-date = January 20, 2021| archive-date = January 17, 2023| archive-url = https://web.archive.org/web/20230117175715/https://support.google.com/mail/community?hl=en&gpf=| url-status = live}}</ref><ref>{{cite web| url = https://answers.microsoft.com/en-us/outlook_com/forum/oemail-ocompose/message-could-not-be-delivered-please-ensure-the/87a52762-7d08-467e-85a2-120721c2dd8e?auth=1| title = Message could not be delivered. Please ensure the message is RFC 5322 compliant.| access-date = January 20, 2021| archive-date = January 28, 2021| archive-url = https://web.archive.org/web/20210128115816/https://answers.microsoft.com/en-us/outlook_com/forum/oemail-ocompose/message-could-not-be-delivered-please-ensure-the/87a52762-7d08-467e-85a2-120721c2dd8e?auth=1| url-status = live}}</ref> [[DomainKeys Identified Mail]], [[Sender Policy Framework]] and [[DMARC]], [[DNSBL]]s and [[Greylisting (email)|greylisting]] to reject or quarantine suspicious emails.<ref>{{cite web| url = https://answers.microsoft.com/en-us/outlook_com/forum/oemail-osend/why-are-the-emails-sent-to-microsoft-account/b64e3e4a-0d93-40c8-8e28-4be849012f9c| title = Why are the emails sent to Microsoft Account rejected for policy reasons?| access-date = January 20, 2021| archive-date = February 14, 2021| archive-url = https://web.archive.org/web/20210214021030/https://answers.microsoft.com/en-us/outlook_com/forum/oemail-osend/why-are-the-emails-sent-to-microsoft-account/b64e3e4a-0d93-40c8-8e28-4be849012f9c| url-status = live}}</ref>