Roll out umbriel as our mailserver (again)

Now that #622 has landed, I believe
we're ready to try this again.

This reverts commit 5a6958d.

Author: jfly

build/pluto/prometheus/exporters/blackbox.nix

@@ -117,14 +117,6 @@ in
           "https://tracker.security.nixos.org"
         ];
       })
-      # TODO: remove this static probe once `umbriel` is our MX record, and
-      # ImprovMX is out of the picture.
-      # https://github.com/NixOS/infra/issues/485
-      (mkStaticProbe {
-        module = "smtp_starttls";
-        job_suffix = "_umbriel";
-        targets = [ "umbriel.nixos.org:25" ];
-      })
       (mkDnsSdProbe "smtp_starttls" {
         names = [
           "nixos.org"

dns/nixos.org.js

@@ -7,26 +7,18 @@ D("nixos.org",
 	TXT("@", "google-site-verification=Pm5opvmNjJOwdb7JnuVJ_eFBPaZYWNcAavY-08AJoGc"),
 
 	// nixos.org mailing
-	MX("@", 10, "mx1.improvmx.com."),
-	MX("@", 10, "mx2.improvmx.com."),
-	// TODO: Replace with the following MX records once we migrate away from ImprovMX
-	//MX("@", "umbriel")
+	MX("@", 10, "umbriel"),
 	SPF_BUILDER({
 		label: "@",
 		parts: [
 			"v=spf1",
-			// TODO: Remove once we migrate away from ImprovMX
-			"include:spf.improvmx.com",
 			"a:umbriel.nixos.org",
 			"~all"
 		]
 	}),
 	DMARC_BUILDER({
 		policy: "none",
 	}),
-	// TODO: Remove once we migrate away from ImprovMX
-	CNAME("dkimprovmx1._domainkey", "dkimprovmx1.improvmx.com."),
-	CNAME("dkimprovmx2._domainkey", "dkimprovmx2.improvmx.com."),
 
 	// discourse
 	A("discourse", "195.62.126.31"),

non-critical-infra/modules/mailserver/README.md

@@ -1,8 +1,6 @@
 # NixOS mailserver
 
-This module will [eventually][issue 485] provide mail services for `nixos.org`.
-
-[issue 485]: https://github.com/NixOS/infra/issues/485
+This module provides mail services for `nixos.org`.
 
 ## Mailing lists