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mail server

Sendmail: Clear / Delete / Flush Mail Queue

How can I permanently delete all e-mail messages in the Sendmail mail server (SMTP) queue using UNIX / Linux command prompt?
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Linux / UNIX: PHP mail() Error Log File

How do I view PHP mail() errors? How do I see php mail() error log file under UNIX or Linux?
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Linux / UNIX: DNS Lookup Command

How do I perform dns lookup under Linux or UNIX or Apple OS X operating systems without using 3rd party web sites for troubleshooting DNS usage?
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I work for a small business and outsourced our email hosting to Google. However, I noticed that spammers are using our From: First Last to send their spam messages. All bounced messages come to our catch only account. How do I stop this? How do I validate our domain using SPF? How do I configure a SPF for Google Apps domain using BIND 9 or djbdns?
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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 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[83.26.101.251]: 554 5.7.1 Service unavailable; Client host [83.26.101.251] 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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What is the difference between authentication and authorization? Why it is important to understand difference between the two? Authentication vs. Authorization -- what are they and how do they differ?
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