Hi. Am 19.11.2014 um 17:56 schrieb Matus UHLAR - fantomas: >> That lead my to the question: WHY is it so bad to have IP addresses in >> MX? > the MX record points to a hostname by definition. > The hostname (and only the hostname) points to address (by definition).
This is not a technical reason. This is kind of "it has to be as it has to be". I don't say that this rule is bullshit or it must be changed. I just wonder why most of the folks out there managed to handle it the other way and courier does not. >> My current example is mail from the Domain "isoloc.com": >> isoloc.com. 600 IN MX 10 217.160.79.52. >> isoloc.com. 600 IN MX 10 smtp.isoloc.com. > there is no TLD named 52. in fact, the MX points to nonexistent host > "217.160.79.52." (see the trailing dot?). It's kind of easy to check if it is an IP address if there is no such TLD. I understand that in time of writing this RFC, it was a valid reason to minimize confusion and to reduce workload for the client. But nowadays, checking a regular expression is really easy in all programming languages. The overhead of the current error handling is potentially higher that it would be to just check if this is an ip address. And additionally: courier could be tolerant if there is one valid and one invalid MX. I like courier to be standards compliant in many ways. But times change and now, we operate one of a really small amount of mail servers that cannot handle this invalid domain. Other can do. So from the sender's perspective, we are the evil ones not to accept their mail. In case of SMTP-SSL failures, there is / was a similar issue but this could always be fixed by an entry in esmtproutes. There is no workaround to manually enable communication in the current situation. - Bernd
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