SMTP-auth via mailx results in service unavailable

Question

Why do my attempts to use mailx with Gandi SMTP fail with 'Service unavailable'?
I have the following ~/.mailrc file which is recognised by mailx:
set smtp=smtps://mail.gandi.net:465
set smtp-auth=login
set smtp-auth-user=harry@XXXXXXX
set smtp-auth-password=XXXXXXX
set from=harry@XXXXXXX
set ssl-verify=ignore
set nss-config-dir=/Users/neville/Thunderbird
The result is below.
From MAILER-DAEMON  Thu Dec 20 15:41:47 2012
Return-Path: <>
X-Original-To: [email protected]
Delivered-To: [email protected]
Received: by G4-N-2.local (Postfix)
          id D4E2DA382D6; Thu, 20 Dec 2012 15:41:47 +0000 (GMT)
Date: Thu, 20 Dec 2012 15:41:47 +0000 (GMT)
From: [email protected] (Mail Delivery System)
Subject: Undelivered Mail Returned to Sender
To: [email protected]
Auto-Submitted: auto-replied
MIME-Version: 1.0
Content-Type: multipart/report; report-type=delivery-status;
          boundary="78E73A382D4.1356018107/G4-N-2.local"
Message-Id: <[email protected]>
This is a MIME-encapsulated message.
--78E73A382D4.1356018107/G4-N-2.local
Content-Description: Notification
Content-Type: text/plain; charset=us-ascii
This is the mail system at host G4-N-2.local.
I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can
delete your own text from the attached returned message.
                   The mail system
<neville@XXXXXXX>: host spool.mail.gandi.net[217.70.184.6] said: 554 5.7.1
    Service unavailable; Client host [XXXXXXX] blocked using
    pbl.spamhaus.org; http://www.spamhaus.org/query/bl?ip=XXXXXXX (in
    reply to RCPT TO command)
--78E73A382D4.1356018107/G4-N-2.local
Content-Description: Delivery report
Content-Type: message/delivery-status
Reporting-MTA: dns; G4-N-2.local
X-Postfix-Queue-ID: 78E73A382D4
X-Postfix-Sender: rfc822; [email protected]
Arrival-Date: Thu, 20 Dec 2012 15:41:47 +0000 (GMT)
Final-Recipient: rfc822; neville@XXXXXXX
Action: failed
Status: 5.7.1
Remote-MTA: dns; spool.mail.gandi.net
Diagnostic-Code: smtp; 554 5.7.1 Service unavailable; Client host
    [XXXXXXX] blocked using pbl.spamhaus.org;
    http://www.spamhaus.org/query/bl?ip=XXXXXXX
--78E73A382D4.1356018107/G4-N-2.local
Content-Description: Undelivered Message
Content-Type: message/rfc822
Received: by G4-N-2.local (Postfix, from userid 501)
          id 78E73A382D4; Thu, 20 Dec 2012 15:41:47 +0000 (GMT)
To: neville@XXXXXXX
Subject: test
Message-Id: <[email protected]>
Date: Thu, 20 Dec 2012 15:41:47 +0000 (GMT)
From: [email protected] (Neville Hillyer)
test email
--78E73A382D4.1356018107/G4-N-2.local--

Answer 1

http://www.spamhaus.org says:
Mail servers only run spam filters such as Spamhaus PBL on port 25, so if you find you are being blocked by the PBL when you try to send mail to your mail server that means you are not communicating with the mail server on the 'authenticated' port 587 but you're still on port 25. This means your 'SMTP Authentication' is not working correctly.
http://wiki.gandi.net/en/mail/standard-settings#smtp-account says:
SMTP Account
Name server : mail.gandi.net
Port : 25, 465 (with SSL) or 587 (try one or the other)
TLS or SSL: yes
SMTP Authentication : yes, using the same settings as for the POP / IMAP account
I was trying to use the same settings I have used for several years with Thunderbird and Apple Mail, ie SSL on port 465.
Is there something wrong with my settings which could be preventing mailx from using port 465?
A few debug tips would be appreciated.
Your link causes me to ask:  Does the mailx on Leopard support SMTP directly?