test_mail: gracefully handled when the server has no reverse DNS available

tests/test_mail.py

@@ -38,13 +38,18 @@ server.starttls()
 # Verify that the EHLO name matches the server's reverse DNS.
 ipaddr = socket.gethostbyname(host) # IPv4 only!
 reverse_ip = dns.reversename.from_address(ipaddr) # e.g. "1.0.0.127.in-addr.arpa."
-reverse_dns = dns.resolver.query(reverse_ip, 'PTR')[0].target.to_text(omit_final_dot=True) # => hostname
-server.ehlo_or_helo_if_needed() # must send EHLO before getting the server's EHLO name
-helo_name = server.ehlo_resp.decode("utf8").split("\n")[0] # first line is the EHLO name
-if helo_name != reverse_dns:
+try:
+	reverse_dns = dns.resolver.query(reverse_ip, 'PTR')[0].target.to_text(omit_final_dot=True) # => hostname
+except dns.resolver.NXDOMAIN:
+	print("Reverse DNS lookup failed for %s. SMTP EHLO name check skipped." % ipaddr)
+	reverse_dns = None
+if reverse_dns is not None:
+	server.ehlo_or_helo_if_needed() # must send EHLO before getting the server's EHLO name
+	helo_name = server.ehlo_resp.decode("utf8").split("\n")[0] # first line is the EHLO name
+	if helo_name != reverse_dns:
 		print("The server's EHLO name does not match its reverse hostname. Check DNS settings.")
 		sys.exit(1)
-print("SMTP EHLO name (%s) is OK." % helo_name)
+	print("SMTP EHLO name (%s) is OK." % helo_name)
 
 # Login and send a test email.
 server.login(emailaddress, pw)