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  1. #1

    error sending mail to some addresses

    Hello! I have Linux RedHat 7.3 with sendmail.
    When I try to send mail to some addresses : (ex:
    I receive:

    The original message was received at Mon, 28 Mar 2005 13:38:29 +0300
    from localhost.localdomain []

    ----- The following addresses had permanent fatal errors -----
    (reason: 501 5.7.1 <>... Sender IP must resolve)

    ----- Transcript of session follows -----
    ... while talking to
    >>> MAIL From:<> SIZE=2174
    <<< 501 5.7.1 <>... Sender IP must resolve
    501 5.6.0 Data format error

  2. #2
    Linux Newbie
    Join Date
    Dec 2004
    Barrie, Ontario
    Most major mail systems (,, etc) require that your IP has a reverse DNS entry. Unless you are on a higher end network connection, you're probably not going to get that.

    That error means that they did a lookup on your IP and it has no FQDN attached to it.
    Blog - KB5UMQ - Linux User #272983
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