Use Qpopper to create a POP3 server in Linux

When you create Sendmail or any other standard SMTP server, it is important to remember that this is the only way to transfer information between your Linux host and other mail servers. In order for your users to retrieve their information, you need to establish a POP3 or IMAP service. Qpopper is a general POP3 implementation option. You can install it and quickly and easily create services. A few simple steps are required.

Install Qpopper using Sendmail

This article describes how to install Qpopper. I will assume that you have installed Sendmail. However, Qpopper will be compatible with any other standard SMTP server.

First, download the latest resource package qpopper4.0.3.tar.gz from the qpopper's website. You will also find a large number of files and software documents on this site. After downloading this version, run the tar xpfz command to decompress it. Create a new directory named qpopper4.0.3 and execute./configure. Then you can start the installation.

If you have used it before, you may have more requirements than the default installation, and are sure to read the documentation to find all editable options. For example, you may prefer to use Qpopper as an independent background email program instead of running it from inetd or xinetd. To do this, you need to run./configure and use the option -- enable-standalone.

When using Qpopper as an independent background program, you need to create a script to start the correct service during import. Qpopper is installed under/usr/local/lib by default unless you install it from a specific version file such as RPM or DEB. If the installation starts from the original resource, you also need to add the following lines in the/etc/inetd. conf file:

Pop3 stream tcp nowait root/usr/local/lib/popper qpopper-s

If you are using xinetd. conf. This is the latest Red Hat 7. x is installed by default, and you are sure to install it in/etc/xinetd. A file named pop3 is created in the d/directory. Its content is as follows:

service pop3 { socket_type = stream protocol = tcp wait = no user = root server = /usr/local/lib/popper server_args = qpopper -s port = 110 }

When you add a new service, first check your firewall filtering rules and the/etc/hosts. allow file. Your Firewall should allow TCP requests to be directly accepted on port 110, which is the POP3 Service port and your hosts. allow file should have ALL rows. Similarly, if it is Red Hat, check/etc/xinetd. d/and make sure there is no existing POP3 server. A standard installation option is used to make the pre-configuration possible. Therefore, if you add Qpopper later, make sure that all such items such as/etc/xinetd have been deleted from the xinetd background program. d/ipop3.

Create Qpopper

Once Qpopper is installed, You need to enable the Service. If you are using inetd or xinetd, you can simply restart the inetd or xinetd background program by executing kill-HUP. You can run ps aux | grep inet to determine the process ID (PID ).

If you have installed Qpopper in standalone mode, you need to place the parameter-S in the/etc/init. d/pop3 file to execute the script you have created. For example, the-S tag tells Qpopper to run in server mode, which can improve the input/output performance of the server. If it is not in server mode, Qpopper will copy the email file based on the priority access principle and copy it back after corresponding adjustments, such as deleting an email. In server mode, Qpopper scans the queue rather than copies and processes them directly in users' tasks. This is especially important for POP3 servers that need to support a large number of users.

When running a POP3 server, Table 1 lists all the command options you can use. For example, you can remotely log on to your server from port 110 and manually delete large information. A comprehensive understanding of these options will help you quickly resolve your email faults.

After this command, enter your user id, such as USER webmaster.

PASS: enter the password for this account.

The QUIT command ends the current task and deletes the marked emails.

The list command can be used to LIST the information and size.

RETR restores a specific email with an information number.

The DELE Command deletes a specific email with an information number.

TOP displays the first N rows of a specific email (TOP <# lines> ).

Qpopper relies on the standard system verification mechanism being applied through/etc/passwd and/etc/shadow. Therefore, to allow users to use the POP3 service, it is necessary to add the service to the local system. Since you may have run an email proxy such as Sendmail, this is actually done.

Discover and solve Qpopper faults

During the first running of any service you install, some problems may occur. A good solution is that the server can respond to POP3 requests logging on to port 110. You can try to log on from a local or remote site. You will see the command line examples in these experiments.

If a large number of users connect to your server to obtain emails, you may need to change the maximum wait value to increase the inetd timeout value. You can do this:

Pop3 stream tcp nowait.400 root/usr/local/lib/popper qpopper-s

When a large number of tasks are running at the same time, this can prevent Qpopper from entering an endless loop. When you start logging in, your log file starts to record the service, and you can change the timeout value I mentioned above.

Another problem is that emails are often locked on large websites. When a client opens a POP3 task to the server, the file will be created when the email is locked. It blocks connections to other modified mailboxes. Sometimes, a user is disconnected abnormally, and Qpopper cannot delete the temporary file queue established at the beginning of the task. This often appears in the/var/spool directory in the form of. user. pop. The server usually detects out-of-date email locks and deletes them. However, in rare cases, administrators may need to manually delete these files to allow re-access to the POP3 server.

Summary

To provide users with the full email function, it is an important step to add the POP3 service to your Sendmail server. Through Qpopper, this task becomes quite simple. Download, install, restart, and run quickly. It can also run with other standard SMTP servers.

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