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APEGamer's avatar
New Contributor
4 years ago

Change Modem IP Address

We just moved to Arizona and switched to Cox cable. Unfortunately, the IP address the modem uses seems to be blocked by Outlook. Both my wife and a co-worker uses and emails to them are returned with the error:

host [ip address here]
SMTP error from remote mail server after pipelined end of data:
550 5.7.1 Unfortunately, messages from [ip address here] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140). You can also refer your provider to []

Microsoft ways they can't see why this address would be a problem, and offered no other real support.

I'd like to change my modem's IP address with the hope that Outlook won't block the new address.

2 Replies

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  • Bruce's avatar
    Honored Contributor III

    Changing your IP won't help because email servers don't operate on user records (you) but with DNS records.  For example, if you're using to send email to, uses DNS to lookup the IP address of  Basically.

    Is the "ip address here" the Cox-assigned public IP address of your modem?
    I'll assume is sending an error to just your account (on somewhere).
    What email service are you using?

    It seems doesn't like the IP address of your email server...not you.  If your email provider changed something within their domain, the DNS "system" doesn't contain the update.  However, this "update" could be anything...such as a Primary DNS server being down while an active Secondary DNS is using an outdated record.  Cox should have at least contacted their email contractor.

  • Bruce's avatar
    Honored Contributor III

    Hmm?  Shot in the dark:  If you just moved, it could be a geographical issue.  From where did you move?

    Long ago, I remember configuring my email program (Outlook), for an email server as an "east" host.  Cox has since stopped using east and west designations but I was still using "east" long after their change.  I only discovered the outdated name when Cox changed their port numbers.

    If you're using a bookmark, check it for any geographical information or just recreate the bookmark.