HTTP/2 302 date: Mon, 14 Jul 2025 00:48:39 GMT content-type: text/html content-length: 143 location: https://get.ietf.org/implementation-report/report-smtp-pipeline.txt cache-control: private, max-age=0, no-store, no-cache, must-revalidate, post-check=0, pre-check=0 expires: Thu, 01 Jan 1970 00:00:01 GMT vary: Accept-Encoding server: cloudflare cf-ray: 95ed04054e0e8839-BLR alt-svc: h3=":443"; ma=86400 HTTP/2 200 date: Mon, 14 Jul 2025 00:48:39 GMT content-type: text/plain etag: W/"718bc8a1d51c8c44c624957565fbab0b" vary: Accept-Encoding server: cloudflare cf-ray: 95ed04056db4c1c7-BLR content-encoding: gzip alt-svc: h3=":443"; ma=86400 Reported by Ned Freed There are a bunch of independent implementations, but I can list two major ones right off: PMDF and software.com's post.office. There's even an implementation of SMTP pipelining in the MUMPS mail system, according to the folks at the USDA.