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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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Google Apps Domain Create SPF Records For BIND or Djbdns

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[]: 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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What Is The Difference Between Authentication And Authorization?

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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Postfix Configure Multiple ISP Client SMTP Authentication

How do I support multiple ISP accounts (smarthost) in the Postfix SMTP client for relaying email? For example:

[a] user1@isp1.com must be relay via smtp.isp1.com.
[b] user1@isp2.com must be relay via smtp.isp2.com.
[c] me@mycorp.com must relay all my default email via smtp.mycorp.com.
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Postfix Configure Client SMTP Authentication ( Smarthost Authentication )

My ISP requires that mail from my dynamic IP to our small business email addresses uses their outgoing SMTP servers. This is probably done to reduce abuse and spam but now I'm not able to send email and local Postfix log file displays authentication failure message. How do I relay mail through my mail ISP servers using Postfix SMTP under Linux / UNIX like operating systems?
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FreeBSD Install FuzzyOCR To Detect Image Spam

How do I install FuzzyOcr plugin for SpamAssassin to detect unsolicited bulk mail (Spam) containing images as the main content for Postfix mail server?
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