电子邮件提供商可能更喜欢它的另一个原因是它进行轮询，很像 RSS 新闻阅读器。 POP 客户端将打开到服务器的 TCP/IP 连接、验证自身身份、请求任何电子邮件并执行所需的任何处理，然后关闭连接。
IMAP 客户端通常在其运行的整个过程中使一个或多个 TCP/IP 套接字与服务器保持打开状态，从而占用这些资源。 这是 ISP 更喜欢 POP 的另一个原因。
Google 邮件支持 POP 和 IMAP 协议。
（PS，我的意思并不是说我在尝试 ISP。我认为我上面归因于他们的原因是非常务实和明智的。）
I think part of it is that IMAP is usually used in scenarios where the emails are retained on the server, whereas POP is used almost exclusively for situations where the email is downloaded to the local machine, which is what most ISPs providing email facilities for their customers want you to do (and also what most of the customers probably want as well, although less so as they get more exposure to the Internet and things like gmail and yahoo, etc.)
Another reason it is probably preferred by email providers is that it does polling, much like an RSS news reader. The POP client will open a TCP/IP connection to the server, authenticate itself, ask for any email and do whatever processing it needs, and then close the connection.
IMAP clients generally keep one or more TCP/IP sockets open with the server the whole time they are running, taking up those resources. Yet another reason for ISPs to prefer POP.
Google mail supports both POP and IMAP protocols.
(P.S. I do not mean to sound like I am having a go at ISPs. I think the reasons I've attributed to them above are very pragmatic and sensible.)
POP3 is private by default (it assumes that you want to delete email off the server after downloading it).
Initially almost all ISPs had tiny storage limits (since their are free large storage email services this matters less now) so deleting emails that you downloaded was a must.
(for completeness - thanks Evan) POP clients open a TCP/IP connection to the server, authenticates itself, asks for any email and does whatever processing it needs, and then close the connection. IMAP clients generally keep one or more TCP/IP sockets open with the server the whole time they are running, taking up those resources.
POP is a much simpler protocol to implement and can handle a greater number of clients with the same amount of resources.
Yahoo mail still does not offer IMAP. My guess is that it's because I'm more likely to use their site than Outlook, meaning I'll have to see their ads.
Many email services (such as those provided by ISPs) only offer a limited size mailbox. This makes it necessary to download your messages to your computer to be able to store the large number of emails that are common these days.
Another reason is POP3 fetchers. You may have a central IMAP mailbox where you want to download mail from all other accounts of yours to keep all your mail in same place. This is usually done with POP3 fetchers which poll your other mailboxes periodically and load mail from there in your primary mailbox.
Although IMAP fetchers do exist, most of fetchers are still POP3-only and if your other mailbox does not support POP3, you may have troubles using a fetcher to link it with your primary mailbox.
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因为POP3不需要服务器端那么多的存储。 而且因为它更简单、更容易实现。
Because POP3 does not need as much storage on the server side. And because it is more simple and easy to implement.
我认为部分原因是 IMAP 通常用于电子邮件保留在服务器上的情况，而 POP 几乎专门用于将电子邮件下载到本地计算机的情况，这也是大多数 ISP 为其提供电子邮件设施的情况。客户希望你做的事情（也是大多数客户可能也想要的事情，尽管随着他们更多地接触互联网以及 gmail 和 yahoo 等，他们的需求会减少）。
电子邮件提供商可能更喜欢它的另一个原因是它进行轮询，很像 RSS 新闻阅读器。 POP 客户端将打开到服务器的 TCP/IP 连接、验证自身身份、请求任何电子邮件并执行所需的任何处理，然后关闭连接。
IMAP 客户端通常在其运行的整个过程中使一个或多个 TCP/IP 套接字与服务器保持打开状态，从而占用这些资源。 这是 ISP 更喜欢 POP 的另一个原因。
Google 邮件支持 POP 和 IMAP 协议。
（PS，我的意思并不是说我在尝试 ISP。我认为我上面归因于他们的原因是非常务实和明智的。）
I think part of it is that IMAP is usually used in scenarios where the emails are retained on the server, whereas POP is used almost exclusively for situations where the email is downloaded to the local machine, which is what most ISPs providing email facilities for their customers want you to do (and also what most of the customers probably want as well, although less so as they get more exposure to the Internet and things like gmail and yahoo, etc.)
Another reason it is probably preferred by email providers is that it does polling, much like an RSS news reader. The POP client will open a TCP/IP connection to the server, authenticate itself, ask for any email and do whatever processing it needs, and then close the connection.
IMAP clients generally keep one or more TCP/IP sockets open with the server the whole time they are running, taking up those resources. Yet another reason for ISPs to prefer POP.
Google mail supports both POP and IMAP protocols.
(P.S. I do not mean to sound like I am having a go at ISPs. I think the reasons I've attributed to them above are very pragmatic and sensible.)
几个原因：
贮存。
假设您要删除
之后从服务器发送电子邮件
下载它）。
存储限制（因为它们是免费的
大容量存储电子邮件服务此
现在不那么重要了）所以删除电子邮件
你下载的那个是必须的。
客户端打开 TCP/IP 连接
服务器对自身进行身份验证，
要求提供任何电子邮件并执行任何操作
处理它需要的，然后关闭
连接。 IMAP 客户端
一般保留一个或多个TCP/IP
与服务器打开的套接字
他们一直在奔跑，采取
增加这些资源。
A few reasons:
storage.
assumes that you want to delete
email off the server after
downloading it).
storage limits (since their are free
large storage email services this
matters less now) so deleting emails
that you downloaded was a must.
clients open a TCP/IP connection to
the server, authenticates itself,
asks for any email and does whatever
processing it needs, and then close
the connection. IMAP clients
generally keep one or more TCP/IP
sockets open with the server the
whole time they are running, taking
up those resources.
雅虎邮箱仍然不提供 IMAP。 我的猜测是，这是因为我更有可能使用他们的网站而不是 Outlook，这意味着我必须看到他们的广告。
Yahoo mail still does not offer IMAP. My guess is that it's because I'm more likely to use their site than Outlook, meaning I'll have to see their ads.
许多电子邮件服务（例如 ISP 提供的服务）仅提供有限大小的邮箱。 这使得您有必要将邮件下载到计算机上，以便能够存储当今常见的大量电子邮件。
Many email services (such as those provided by ISPs) only offer a limited size mailbox. This makes it necessary to download your messages to your computer to be able to store the large number of emails that are common these days.
另一个原因是 POP3 获取程序。 您可能有一个中央 IMAP 邮箱，您希望从您的所有其他帐户下载邮件，以便将所有邮件保存在同一个位置。 这通常是通过 POP3 获取程序完成的，它会定期轮询您的其他邮箱并将邮件从那里加载到您的主邮箱中。
尽管 IMAP 提取器确实存在，但大多数提取器仍然仅支持 POP3，如果您的其他邮箱不支持 POP3，则使用提取器将其与主邮箱链接时可能会遇到问题。
Another reason is POP3 fetchers. You may have a central IMAP mailbox where you want to download mail from all other accounts of yours to keep all your mail in same place. This is usually done with POP3 fetchers which poll your other mailboxes periodically and load mail from there in your primary mailbox.
Although IMAP fetchers do exist, most of fetchers are still POP3-only and if your other mailbox does not support POP3, you may have troubles using a fetcher to link it with your primary mailbox.