20 questions about Postfix

Source: Internet
Author: User
Tags sender policy framework

20 questions about Postfix

Question 1: What is Postfix and what is its default port?

A: Postfix is an open-source MTA email delivery Agent. It is used to forward emails. I believe many people know about Sendmail, and Postfix is a substitute for Sendmail. The default port is 25.

Question 2: What is the difference between Postfix and Sendmail?

A: Postfix uses a modular design consisting of multiple independent executable programs. Sendmail is designed to have a powerful background process to provide all services.

Question 3: What is MTA and what role does it play in the mail system?

A: MTA is the abbreviation of Mail Transfer Agent. MTA is responsible for receiving and sending emails, determining the sending path and address rewriting LCTT: address rewriting, is to improve the Sending address, such as rewriting the "username" address as "username@example.com "). Local forwarding means sending emails to MDA. Qmail, Postix, and Sendmail are all MTA.

Question 4: What is MDA?

A: MDA is short for Mail Delivery Agent. This program is used to get the message from MTA and deliver it to the mailbox of the local recipient. MDA can usually filter emails or classify them. One MDA can also determine whether an email needs to be forwarded to another email address. Procmail is an MDA.

Question 5: What is MUA?

A: MUA is the abbreviation of Mail User Agent. MUA is an email client software that can be used to write, send, and receive emails. The message is sent using MTA. You can receive the message directly from the mail storage area or indirectly through the POP/IMAP server. Outlook, Thunkerbird, and Evolution are all MUA.

Question 6: What is the role of postmaster in the mail server?

A: Generally, the email manager is postmaster. A postmaster is responsible for ensuring the normal operation of the mail system, updating system configurations, adding/deleting email accounts, and other work. Each domain must have a postmaster alias LCTT. Note: The postmaster alias is used to receive communication emails from other servers/users about the email system, such as complaints about rejection of spam emails, it is usually directly accepted by the email server administrator. Some emails with system errors and prompts often use postmaster as the sender), which is used to send emails to the correct users.

Question 7: What are the important processes in Postfix?

A: The following lists the most important background processes in the Postfix email system:

  • Master: This process is the brain of the Postfix mail system, which generates all other processes.
  • Smtpd: Serves as a server program to process all external connection requests.
  • Smtp: Process all requests that initiate external connections as a client program.
  • Qmgr: It is the heart of the Postfix mail system, processing and controlling all messages in the mail queue.
  • Local: This is Postfix's local delivery agent MDA, which is responsible for saving emails to the mailbox.
Question 8: What is the configuration file of the Postfix server?

A: There are two main configuration files:

  • /Etc/postfix/main. cf: This File Stores global configuration information, which will be used by all processes unless these configurations are reset in the master. cf file.
  • /Etc/postfix/master. cf: This File Stores additional process runtime environment parameters. The configuration defined in the main. cf file may be overwritten by the configuration in this file.
Question 9: How can I restart the Postfix and set it to boot?

A: Use this command to restart: service postfix restart; Use this command to set it to boot: chkconfig postfix on

Question 10: how to view the Postfix message queue?

A: Postfix maintains two queues: pending mails queue and waiting for deferred mail queue ). The waiting queue contains the emails that failed to be sent temporarily and need to be resending. The default value of Postfix is 5 minutes. You can customize the settings ). LCTT note: In fact, Postfix maintains five Queues: the input queue, the mail enters the first stop of the Postfix system; the activity queue, qmgr move the entered queue emails to the activity queue; wait queue, saves emails that cannot be sent out for the time being; fault queues, stores damaged or uninterpreted emails; keep queues, and keep emails in the Postfix Queue System for an indefinite period of time .)

List all emails in the mail queue:

  1. # postqueue -p

Save the mail queue list:

  1. # postqueue -p > /mnt/queue-backup.txt

Let the Postfix process the queue immediately:

  1. # postqueue -f
Question 11: How do I delete emails in a mail queue?

A: run the following command to delete all Emails:

  1. # postsuper -d ALL

Run the following command to delete only emails in the waiting queue:

  1. # postsuper -d ALL deferred
Question 12: How can I check the Postfix configuration through a command?

A: You can run the postconf-n command to check the configuration information commented out in the configuration file.

Question 13: What command should I use to view mail logs in real time?


  1. Tail-f/var/log/maillog or tailf/var/log/maillog
Question 14: How can I send a test email through the command line?

A: refer to the following command:

  1. # echo "Test mail from postfix" | mail -s "Plz ignore" info@something.com
Question 15: What is "Open Mail forwarding Open Relay )"?

A: Open Mail forwarding is a configuration of the SMTP server, which allows any other users on the Internet to forward emails through this server, instead of sending emails directly to the server of an account or only allowing authorized users to send emails. In the past, this feature was enabled by default on many mail servers, but it is no longer popular, because Email Forwarding can cause a large number of spam and virus emails to go viral on the Internet.

Question 16: What is the mail forwarding host on Postfix?

A: The forwarding host is the SMTP address. If it is configured in the configuration file, all input emails will be forwarded by the SMTP server.

Question 17: What is a gray list?

A: The gray list LCTT between the White List and the Black List) is a technology used to block spam. When an MTA uses a gray list, it will "temporarily reject" all emails sent from unrecognized senders. If the email is justified, the initiator will resend the email after a period of time and the email will be accepted. The gray list is based on the fact that most spam servers and botnets send emails only once, the requests that require them to be sent again after a certain interval are ignored .)

Question 18: What is the important role of SPF records in the mail system?

A: SPF is short for the Sender Policy Framework. It is used to help the mail domain owner determine whether the Sender is from their domain, the purpose is that other email systems can ensure that the sender is sent from an authorized source-this method can reduce the risk of email address spoofing, phishing, and spam.

Question 19: what is the use of DKIM in the email system?

A: The domain name key is an email identity authentication system used to verify the DNS domain and email integrity of the email sender. The domain name key specification adopts Internet email authentication technology and establishes an enhanced protocol: The domain name key recognition email is DKIM ).

Question 20: What are the ASSP rules in the mail system?

A: ASSP (Anti-Spam SMTP Proxy, Anti-Spam Proxy) is a gateway server installed in front of your MTA, through self-built whitelist, automatic Learning Bayesian algorithm, gray list, DNS blacklist DNSBL), DNS whitelist DNSWL), URI blacklist URIBL), SPF, SRS, Backscatter, virus scanning, attachment blocking, and anti-spam based on senders.

Via: http://www.linuxtechi.com/postfix-interview-questions-answers/

Author: Pradeep Kumar Translator: bazz2 Proofreader: wxy

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