Support RFC 7505 "null MX" (#702) (#703)

* Fix #702: Spurious null MX changes on CloudFlare

* Test roundtripping null MX on Cloudflare

* Use an if instead of TrimSuffix

* Add other providers that support RFC 7505

* Suppress test for non-compliant providers

integrationTest/integration_test.go

@@ -609,6 +609,11 @@ func makeTests(t *testing.T) []*TestGroup {
 			tc("Record pointing to @", mx("foo", 8, "**current-domain**")),
 		),
 
+		testgroup("Null MX",
+			not("AZURE_DNS", "GANDI_V5", "NAMEDOTCOM", "DIGITALOCEAN"), // These providers don't support RFC 7505
+			tc("Null MX", mx("@", 0, ".")),
+		),
+
 		testgroup("NS",
 			not("DNSIMPLE", "EXOSCALE"),
 			// DNSIMPLE: Does not support NS records nor subdomains.

providers/cloudflare/cloudflareProvider.go

@@ -541,7 +541,9 @@ type cfRecord struct {
 func (c *cfRecord) nativeToRecord(domain string) *models.RecordConfig {
 	// normalize cname,mx,ns records with dots to be consistent with our config format.
 	if c.Type == "CNAME" || c.Type == "MX" || c.Type == "NS" || c.Type == "SRV" {
-		c.Content = dnsutil.AddOrigin(c.Content+".", domain)
+		if c.Content != "." {
+			c.Content = c.Content + "."
+		}
 	}
 
 	rc := &models.RecordConfig{