sendmail: bugfix: set remote hostname to verify for tls connections

due to logic bug we weren't setting it, and tls connections would fail with a
warning that either the remote hostname must be set or insecurityskipverify
must be set.

sendmail.go

@@ -274,7 +274,7 @@ binary should be setgid that group:
 	xsavecheckf(err, "parsing our local hostname")
 
 	var remoteHostname dns.Domain
-	if net.ParseIP(submitconf.Host) != nil {
+	if net.ParseIP(submitconf.Host) == nil {
 		remoteHostname, err = dns.ParseDomain(submitconf.Host)
 		xsavecheckf(err, "parsing remote hostname")
 	}