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EMail Servers

Q. I've recently changed email user account password using passwd command, for one my postfix email server which requires SMTP authentication before sending an email. Now following error is logged into my /var/log/maillog file:

ERROR: Password not accepted from server: 535 5.7.0 Error: authentication failed: authentication failure

How do I solve this problem under Red Hat enterprise Linux running Postfix with SASL authentication?
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How do I restart dovecot IMAP4 / IMAP (Internet Message Access Protocol) under RHEL / CentOS / Fedora / Debian / Ubutnu Linux?
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Dedicated Server Hosting

Q. We have decided to move to Linux and brought a dedicated Dell server preinstalled with Red Hat Linux for hosting our small business website. Can you tell me what software required to run on a Linux dedicated server for hosting purpose?
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Mail delivery: DNS: Service unavailable error

Q. My mail delivery fails with DNS: Service unavailable error. How do I fix this error under Linux / UNIX operating systems?
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Q. I get following error message for my postfix email server:

Mail Delivery Failed With DNS Service Unavailable Error and Solution

How do I fix this problem?
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Q. Can you tell me more about Linux Demilitarized Zone and Ethernet Interface Card Requirements for typical DMZ implementation? How can a rule be set to route traffic to certain machines on a DMZ for HTTP or SMTP?

A. Demilitarized zone, used to secure an internal network from external access. You can use Linux firewall to create DMZ easily. There are many different ways to design a network with a DMZ. The basic method is to use a single Linux firewall with 3 Ethernet cards. The following simple example discusses DMZ setup and forwarding public traffic to internal servers.
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Delete all root mail / inbox from a shell prompt

Q. I've CentOS Linux acting as router for our small community based college. I see logwatch and other cron job generating emails for root account. How do I delete those emails? I don't want to disable email facility but just wanted to get rid of all root emails.

A. The easilst way is to empty root / users email message file i.e. /var/spool/mail/root or /var/spool/mail/username. Simply type the following command at shell:
> /var/spool/mail/root