mail server HowTo - Linux / Unix Q & A from nixCraft

Sendmail: Clear / Delete / Flush Mail Queue

last updated July 1, 2011 in UNIX

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

Linux / UNIX: PHP mail() Error Log File

last updated November 12, 2010 in Linux, PHP, UNIX

How do I view PHP mail() errors? How do I see php mail() error log file under UNIX or Linux?

Linux / UNIX: DNS Lookup Command

last updated January 14, 2014 in Commands, Linux, UNIX

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?

Google Apps Domain Create SPF Records For BIND or Djbdns

last updated October 22, 2010 in Bind dns, UNIX

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?

Start / Stop / Restart Postfix Mail Server

last updated June 23, 2011 in EMail Servers

How do I start / stop / restart my postfix mail server under Linux or UNIX operating systems?

SPAMHAUS BLOCKLIST ADDRESS IS WRONG MUST FIX Error and Solution

last updated May 7, 2009 in EMail Servers, Linux, Networking, RedHat and Friends, Troubleshooting, UNIX

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?

What Is The Difference Between Authentication And Authorization?

last updated February 28, 2012 in CentOS, Debian / Ubuntu, FreeBSD, Linux, RedHat and Friends, Suse, Troubleshooting, Ubuntu Linux, UNIX, Windows

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?