General ideas and methods for fast email fault detection (2)

PreviousArticleI said, how to determine whether DNS is faulty and how to obtain the MX record of the domain name of the other party. If we can obtain the above information correctly, it means that this type of problem does not exist. Then we proceed to the next detection.

This chapter describes how to use Telnet to detect the mail server running the Simple Mail Transfer Protocol (SMTP) Service to solve SMTP communication problems. By default, the SMTP listening port is 25.

Before starting a telnet session, you must have the complete SMTP email address of the target user to send the test email. The email address must be in the following format:
User@Site.Domain.com
In this example:
Abc@163.com

We have used NSLookup to obtain the Internet Mail exchanger record 163.com: mx.mail.163.com

In the CMD window, type:

C: \> Telnet mx.mail.163.com 25

Telnet format: Telnet server name and port number

Obtain the following information:

220 coremail SMTP (Anti Spam) system (163com [20050206])

Although the information after message 220 may vary with the running mail server software, if the SMTP service is running and started properly, the message 220 is displayed. Therefore, if you have obtained 220 information, it indicates that you have successfully connected to the server.

If you get other information, such:
Cocould not open connection to the host, on port 25: Connection Failed
Other information indicates that the email service of the recipient is faulty, for example, the server is running and the related service is not started. The email fails to be sent.

Assuming that the fault does not exist now, we get 220 information. We will further detect faults.

Note:
1. Microsoft Telnet does not allow you to use the backspace key. If an error occurs while typing, you must press enter to start typing a new command.
2. Some Telnet applicationsProgramYou must enable the local ECHO function to view the commands you have typed. To perform this operation in a Microsoft Telnet session, type set local_echo at the command prompt.
In Microsoft Windows XP, type set localecho instead of set local_echo.
3. Prompt: 500 command not recognized
Check the command and type it again, or verify that you are communicating directly with the Microsoft SMTP server.

Follow my instructions to observe the following steps. The black part shows the result, and I wrote the description in brackets:

220 coremail SMTP (Anti Spam) system (163com [20050206])

Helo me.com
[Helo is a verb in the SMTP verb set. me.com tells him that he will communicate with him with me.com.]

250 mx11

[If it is normal, a 250 message is displayed. The possible failure is: me.com blocked. indicates that your domain name has been blocked by the server and cannot send emails to it. Solution: communicate with the administrator of the other party to release the domain name.]

Mail from: mymail@me.com

[Mail from: Tell him who the sender is:Mymail@me.com Note: Some email servers perform reverse detection on the email address, so try to use the existing Email address as much as possible. Otherwise, an error may be prompted.]

250 OK

[If it is normal, a 250 message is displayed. The possible failure is: XXX blocked/refused, which indicates that your domain name or email address has been blocked by the server and cannot be sent to him. Note: software such as Norton SMTP gateway can set domain names and spam filtering. They will refer to databases of some large spam management organizations. If your IP address has been included, then these email servers will automatically block your email. Solution: communicate with the administrator of the other party and add the domain name or email address to the exception for approval, or contact the spam management organization to unlock the IP address.]

Rcpt to: abc@163.com

[If this email address exists in the domain, a 250 message is returned. Otherwise, the 550 message is as follows:]

550 <abc@163.com>: invalid user

[Here, we get our fault that the abc@163.com does not exist or is disabled so we cannot send an email to him. Troubleshooting. Follow these steps to use Telnet to send an email directly to an email address.]

Rcpt:Webmaster@163.com

250 OK

Data

[The email content below]

354 end data with <CR> <LF>. <CR> <LF>[If the message content is prompted to end with "." (full stop) + press enter]

Subject: Test mail form me.com

[Subject: indicates the mail title. Press ENTER twice (why? See related SMTP documents) and then enter the mail body.]

As the title.

.[Enter a. number after a carriage return. It must be available]

250 OK: queued as skdbjdx3u0ipfdsf. 1

[The email has been placed in the sending queue, and some servers send it directly]

Quit

No. [exit Telnet]

221 bye

Connection to host lost.

Okay. Through the above steps, we can basically see whether there is a fault in sending emails to all links. If you still cannot send emails to this email address through outlook or other software, it indicates that the fault exists with other parts. We will not discuss it here. Keep up with the later comrades.

Section 3 describes how to test whether the POP3 protocol works properly.

Setup question: is it my problem or a server problem that the POP3 Protocol cannot be used to receive emails?