On Mon, Sep 13, 2010 at 11:54:36PM +0800, Richard Chapman wrote:
>>> relayhost = smtp.gmail.com:submission
>>
>> That should probably be:
>>
>> relayhost = [smtp.gmail.com]:submission
>>
>> I don't think that "smtp.gmail.com" is intended to be an MX RRset.
>
> I'm afraid I don't understand the distinction between the syntax
> "smtp.gmail.com" and "[smtp.gmail.com]" and I'm not familiar with the term
> "MX RRset" either.
Read the "SMTP DESTINATION SYNTAX" portion of:
http://www.postfix.org/smtp.8.html
Without "[]" the domainname specified is first subjected to DNS MX
lookups. This is required when sending mail to a domain, but is
typically wrong when resolving the address of a submission host.
> Can you point me to a document discussing these issues? Strangely (perhaps)
> - the above relayhost directive appears to be doing what I intended it
> to...
Any book that covers the DNS background for operating a mail server.
The Sendmail and Postfix books cover this.
While leaving out the "[]" often works, it can break when MX records
are introduced for the submission host (perhaps via a wildcard in
the parent domain).
--
Viktor.
