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:<postmaster@that.domain>
  RCPT TO:<your.address@that.domain>

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 Matti Aarnio 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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