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Dynamic DNS & problems RECEIVING from hotmail

  •  03-06-2016, 0:52

    Dynamic DNS & problems RECEIVING from hotmail

    I run Mercury 4.8 on my home ADSL line. I've recently changed ISPs and my new ASP doesn't allocate static IPs. So I've registered with duckdns.org and have a subdomain there that they point to my IP, updating if it changes (so far it hasn't).

    Since it's dynamic IP, it's listed in spamhaus.zen, and there's nothing I can do about that, so my outgoing mail goes through a smarthost belonging to a hosting company I have an account with. That's working fine.

    The problem I didn't expect is that some email from at least two Hotmail users is only getting to getting to me intermittently. The senders are getting errors of the form:

    Reporting-MTA: dns;BLU004-OMC2S29.hotmail.com
    Received-From-MTA: dns;BLU437-SMTP52
    Arrival-Date: Sat, 5 Mar 2016 13:39:27 -0800
    Final-Recipient: rfc822 xxxx@mydomain.co.uk
    Action: failed
    Status: 5.5.0
    Diagnostic-Code: smtp;550-Please turn on SMTP Authentication in your mail client. 
    550-blu004-omc2s29.hotmail.com [65.55.111.104]:50245 is not permitted to relay
    550 through this server without authentication.

     The first time this happened, the senders second attempt was delivered, and he'd thoughtfully attached the error from the first try. It looked to me like the hotmail server bouncing it back to him, so I assumed it was temporary error and had been fixed. But it's happened again, with a completely different sender, and several times in a row with the original sender. It still looks like a hotmail error, and I can't find any trace of the event in my MercuryS logs (I've now enabled session logging but didn't then) but it didn't happen before I changed to a dynamic IP, and a bit of Google searching suggest that others have had this problem, and a suspicion that it's caused by an ambiguity in the receiving servers DNS records.

    Since I have a dynamic IP, and my MX record points to my duckdns.org subdomain, I assume my DNS records may look incorrect; I don't think I can have a valid reverse DNS in this situation.

    I wondered if Hotmail is trying to validate my address and failing, so bouncing the email as a public service, and since I don't think there's a proper code for "rejected because I've decided the final recipient won't want it" is quoting spurious grounds. It wouldn't be the first time I've had an Microsoft originated error message that didn't match the actual error.

    I have both my real domain and my dynamic subdomain on the right hand side in mercury.ini, and my real domain in the canonical name (maybe I should use the dynamic subdomain?).

    Suggestions gratefully received. Thank you.

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