2019-7-24 · 邮箱发送提示Could not connect to SMTP host: smtp.163.com, port: 465看上去 是 smtp.163.com 的 465 端口 无法连通。实际在服务器测试时，465端口是正常的。 反而是 25端口无法连通。阿里云服务器 的 25端口是默认没开。需要申请开通即可。转载于:https

Port 25: SMTP port 25 continues to be used primarily for SMTP relaying. SMTP relaying is the transmission of email from email server to email server. In most cases, modern SMTP email clients (Microsoft Outlook, Mail, Thunderbird, etc.) shouldn't use this port. Port 25 is actually a virtual port coined somewhere near 1982. There was a Request for Comments (RFC) 821 was published, to add port 25 as the default gateway to send and receive emails. It has been 3 decades and we are still using port 25 as the default port for transmitting email messages. For Gmail to send mail from an email program like Outlook or Thunderbird, the program needs to understand how to communicate with Gmail's email servers. It does this through Simple Mail Transfer Protocol (SMTP) server settings. The settings are the same for any email provider you use with Gmail. Many email clients and services use port 25 for SMTP to send out emails. However an ISP (Internet Service Provider) may block port 25 in order to prevent spamming by its customers. This article will show you how you can check to see if Port 25 is blocked on your network.

How to enable IMAP/POP3/SMTP for Google Accounts

Commonly mailhosts are named mail.domain.com # The example will fit if you are in domain.com and your mailhub is so named. mailhub=mail # Example for SMTP port number 2525 mailhub=smtp.gmail.com:465 # Example for SMTP port number 25 (Standard/RFC) # mailhub=mail.your.domain # Example for SSL encrypted connection # mailhub=mail.your.domain:465 Many ISPs are now blocking port 25. If you are unable to send email but are able to receive, you may need to change your outgoing SMTP server port to 26. Here are the related instructions for the most popular email clients: Thunderbird To change the outgoing mail port from 25 to 26: Launch the Thunderbird mail client

This makes it easy to simulate a mail client with the telnet command to check the access to port 25. The following steps are required on a Linux command line: Execute telnet SERVERNAME 25. This connects telnet to port 25 on the server with the name SERVERNAME.

2014-8-18 · 25端口（SMTP）：25端口为SMTP（Simple Mail Transfer Protocol，简单邮件传输协议）服务所开放的，是用于发送邮件。 如今绝大多数邮件服务器都使用该协议。当你给别人发送邮件时，你的机器的某个动态端口（大于1 How to use Gmail as your SMTP server - Lifehacker