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From "Richard O. Hammer" <ROHam...@EarthLink.net>
Subject Re: Regarding BUG 24885: RemoteDelivery only tries one of multiple A record
Date Fri, 05 Dec 2003 23:22:09 GMT
Noel J. Bergman wrote:
> Søren Hilmer wrote:
...
>>>So it is handling a multihomed destination that needs to be addressed.

I want to make sure I understand this issue.  I've put some debugging 
statements into org.apache.james.dnsserver.DNSServer, which print out 
Record.toString() in places of interest.  Today, when I call 
findMXRecords("yahoo.com"), the subsequent lookup("yahoo.com", 
Type.MX); returns the following three records, shown here before they 
are sorted for priority order.

    yahoo.com.  2320	IN	MX	1 mx2.mail.yahoo.com.
    yahoo.com.  2320	IN	MX	5 mx4.mail.yahoo.com.
    yahoo.com.  2320	IN	MX	1 mx1.mail.yahoo.com.

The problem being discussed here is that host mx2.mail.yahoo.com. may 
exist at several IP addresses (i.e., that a subsequent lookup of 
mx2.mail.yahoo.com. may produce several A records.)(?)  So that if, 
after sorting for priorities, we decide to connect to 
mx2.mail.yahoo.com. , then we need to try each of the IP addresses for 
mx2.mail.yahoo.com. before we go on to try the next host-name in our 
priority ordering (which would be mx1.mail.yahoo.com.)  Is that the 
problem?

Do we know for sure that the JavaMail code underlying the call:
   transport = session.getTransport(urlname);
(in method RemoteDelivery.deliver(Mail, Session)) does not do this for us?

Do you have an example, Søren, of a MX host which you know has 
multiple A records, so that I can test with it?

> The return is a Collection of String objects.  Each one is currently of the
> form "host", but if we were to handle multi-homed hosts by using "host/IP",
> it seems to me that we could either parse it directly  ...

I guess this may require an additional call to the underlying 
DNSServer.rawDNSLookup(), because I don't think 
DNSServer.findMXRecords() ever has the redundant A records.  This is 
interesting -- but with my ignorance of DNS I am just guessing.

Rich



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