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restart postfix

Start / Stop / Restart Postfix Mail Server

How do I start / stop / restart my postfix mail server under Linux or UNIX operating systems?
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I've multiple virtual domain hosted on CentOS Postfix server. How do I forward selected virtual domain email to yahoo / gmail or other email account using Postfix email server?
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I've central mail server gateway. All of our internal systems through this box. How do I remove or hide the hostnames and IP addresses of our internal systems from the messages headers before they go out to other users for security purpose?
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I've configured RBL for my postfix based mail server and I'm getting an error that read as follows:

May 3 04:35:37 mx02 postfix/smtpd[10956]: NOQUEUE: reject: RCPT from ant251.neoplus.adsl.tpnet.pl[]: 554 5.7.1 Service unavailable; Client host [] blocked using xen.spamhaus.org; SPAMHAUS BLOCKLIST ADDRESS IS WRONG MUST FIX; from= to= proto=ESMTP helo=

How do I fix this problem?
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I can send and receive mail using user@example.com, but system generated emails such as root@mail.example.com bounce backup with an error:

May 1 03:14:52 mail postfix/smtp[62798]: 23CA4BD6B40: to=, relay=none, delay=0.01, delays=0/0/0/0, dsn=5.4.6, status=bounced (mail for mail.example.com loops back to myself)

How do I fix this error?
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According to RFC2821 the lowest-numbered records are the most preferred MX for domain. So I've a target Postfix backup server to keep the messages in a queue waiting for the primary server to become available. This ensures that if my primary MX goes down I do not loss any emails. However, spammers are connecting to my backup MX to avoid anti spam filters that are running on the primary MX server. This also hides their real IP from my primary MX. How do I configure anti-spam for my backup RHEL / CentOS 5.3 based Postfix mx server?
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Postfix block PDF or ZIP files attachments

Q. How do I block all PDF or ZIP files attachments under Postfix Mail Server?

A. You can easily block email attachments using mime header check.

Open postfix config file

Login as the root, enter:
# vi /etc/postfix/main.cf

Block zip or pdf files

Use mime_header_checks postfix config directive, enter:
mime_header_checks = regexp:/etc/ostfix/block_attachments
Save and close the file. Open /etc/ostfix/block_attachments file and append code as follows:
/name=[^>]*\.(pdf|zip)/ REJECT
Save and close the file.

Restart Postfix MTA

You must restart or reload postfix:
# /etc/init.d/postfix reload