Interactive DNS MX-verify CGI running at 3 different network locations
Enter here the domain, or email address for which you want to have
the backup delivery things verified.
Further usage guidance below the alternate entry boxes.
Domain or Email Address: (server at kv9.fi network)
Domain or Email Address: (server at funet.fi network)
Domain or Email Address: (server at vger.kernel.org host; With TCP/ECN!)
The domain name (of address!) you give below must have MX records at it.
If there are no MXes for given domain, email might get delivered
by means of using traditional ``if there are no MXes, use A'' operational
rule in the internet. However this utility won't (naturally) have
any usefull work in that case, and it reports an error (but continues..)
This does not send any email to you, just does a series of
connections, plus interactive reception address tests of following kind:
MAIL FROM:<>
RCPT TO:<
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>
RCPT TO:<
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>
The explanation:
- The ``MAIL FROM:<>'' is RFC 821 defined error message transport,
which many systems fault -- they must not do so.
- And every email receiving domain must have postmaster
account, so says RFC 822 standard.
- And finally (if you have given an address, and not just a domain), also
tries to use the address you gave.
For each server, it is acceptable to yield:
- ``ERROR: Connection Timed Out'' -- server wasn't reachable within tester's short 20 second timeout period; this may be due to firewall blocking access to the primary servers with an intention that incoming email comes thru backup servers only. (More usual connection timeout is 5-10 minutes.)
- ``ERROR: Connection Refused'' -- either the destination server does not have SMTP server running, or network firewall near the destination server blocks access to it with an intention of quicker move to backup MX entries.
- ``Apparently OK'' -- the address tests gave an OK result.
Anything else means you have to figure out, what is going on.
Especially if any backup server rejects the ``RCPT TO'' with 400- or 500-series
codes.
All tests this CGI does must yield ``Apparently OK'' if you aspire
to have any change at having reliably working incoming email.
(or ``Connection Timeout'' or ``Connection Refused'' if your primary
server(s) are firewalled, and all traffic must always go via backup servers.)
This CGI utility is one of ZMailer
auxiliary utilities, and it was written by
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after he got sufficiently annoyed about failing
backup-MX servers for lots of different domains
giving reports of type:
- ``not relaying to that domain''
- ``you are not allowed to relay to that domain''
- ``this is not our relaying customer''
- ``sorry, that domain isn't in my list of allowed rcpthosts''
- ``This target address is not our MX service client.''
most common of which are rather misleading wordings about what is going on;
that the server administrator has not listed allowed relay destinations
into some file...
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