Using on IMAP4

What are IMAP4?

This section will give a simple explanation of what IMAP4 are.

Protocol	Strengths	Weaknesses
IMAP4	As you view emails from the server directly, it uses the same environment no matter which computer you access it from. It can also be linked with the web-based email status. This is suited for relatively stable Internet connections.	You cannot view your emails if you cannot connect to the network (some email software will save emails in their cache, meaning you can read them).

IMAP4 have a number of restrictions when using the new system (Gmail).

You can only use IMAP4s (IMAP4 over SSL), and SMTPs (SMTP over SSL). You cannot use unencrypted IMAP4, or SMTP. In other words, you cannot use email software that does not support IMAP4s, or SMTPs.
You need authentication (SMTP auth) when sending emails. You cannot use email software that does not support SMTP auth.
imap.gmail.com do not support the changeover to encrypted transmission using STARTTLS.
When sending emails from an email client using a keio.jp domain address, please be sure to use the SMTP server specified on this page. Due to anti-spam measures (SPF/DKIM/DMARC), emails sent through other SMTP servers may not be delivered.

	Server name	Port	Protocol	Remarks
IMAP4 server	imap.gmail.com	993	IMAP4 (SSL/TLS)
SMTP server	smtp.gmail.com	465/587	SMTP (SSL/TLS)	authentication required (SMTP auth）

When connecting to Port 465 on smtp.gmail.com, you will need to use SSL/TLS when starting transmission, but when connecting to Port 587, you do not use SSL/TSL when starting transmission, but need to switch to STARTTLS from when you first connect.
When setting up your email software, include all of "@keio.jp" in your authentication account.

2015/03/06: First created

2026/07/16: Removed POP3 descriptions and other corrections

Last-Modified: July 16, 2026

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