[Info-vax] SMTP server using port 587 outgoing?

[Stephen Hoffman]

On 2014-09-12 11:18:41 +0000, glen herrmannsfeldt said:

> Stephen Hoffman <seaohveh at hoffmanlabs.invalid> wrote:
> 
>> One of the smaller ISPs I was dealing with was filtering by destination 
>>  DNS, based on empirical evidence.  Messages destined for a mail server 
>>  with a bad DNS configuration were being (silently!) dropped.  Once DNS 
>>  was corrected (and the TTLs expired on the cached data), the mail  
>> messages commenced arriving at the mail server.  (What mail server this 
>>  ISP might have been using, I don't know.)
> 
> There are some rules regarding MX, CNAME, and forwarding that I don't 
> remember right now. If you get them wrong, then the server keeps 
> forwarding to itself.

I'm aware of the mail server setup.

> But normally hosts don't reverse DNS on themself to verify a connection.

This was a DNS check from a mail server of the remote SMTP server's 
DNS, prior to sending the message to the DNS server.  Not of itself.

Though the mail servers I work with do check their own DNS, and do get 
confused when DNS is inconsistently configured.  That's separate from 
what was observed.


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