Use telnet to log on to the smtp service and send an email

Today, I was unaware that someone else posted a post in a forum. using TELNET to connect to the mail server can forge the mail address, so I carefully read how to use TELNET to send emails.
I tested that both QQ and 163 were successfully sent, but the forged address was not enough. This article does not focus on that ....
First, you must use BASE64 to encrypt the user name and password used to log on to your mailbox.
You can use this website to encrypt http://tool.chinaz.com/Tools/base64.aspx online
Then
Telnet smtp.qq.com 25
Start Input
Helo xiaoyu
Auth login
EGlhb3l1 (encrypted user name xiaoyu)
EGlhb3l1 (encrypted password xiaoyu)
Mail from: <76126128@qq.com>
Rcpt to: <8454051@qq.com>
Data
From: 76126128@qq.com
To: 8454051@qq.com
Subject: test
 
Test
 
. (The last decimal point must be added. below is)


 
Status Code Description:
220: Service ready
250: The request email is correct and completed (HELO, mail from, rcpt to, QUIT command execution will return this message)
235: certified
221: Processing
354: Start sending DATA and end with. (This message will be returned if the DATA command is executed successfully)
500: syntax error. The command cannot be identified
550: The command cannot be executed, and the email address is invalid.
552: interrupt handling: the user exceeds the file space
Tags: telnet login smtp service mail