Email server settings
IIJ4U SMTP, IMAP & POP3 settings
Use these settings to add your IIJ4U account (dd.iij4u.or.jp, ff.iij4u.or.jp, hh.iij4u.or.jp …) to Outlook, Apple Mail, Thunderbird, your phone or any app that sends email over SMTP.
Incoming mail
POP3
- Server
- mbox.iij4u.or.jp
- Port
- 110
- Security
- STARTTLS
- User name
- %EMAILLOCALPART%.%EMAILDOMAIN%
- Authentication
- Encrypted password
Outgoing mail
SMTP
- Server
- mbox.iij4u.or.jp
- Port
- 587
- Security
- STARTTLS
- User name
- %EMAILLOCALPART%.%EMAILDOMAIN%
- Authentication
- Encrypted password
How to set up IIJ4U in a mail app
- Choose add account → manual setup (or "other account") in your mail app.
- Enter your full IIJ4U email address and password.
- Pick POP3 for incoming mail and enter the server, port and security from the table above.
- Enter the SMTP server for outgoing mail (mbox.iij4u.or.jp, port 587) and enable authentication with the same login.
If the login keeps failing, enable IMAP/POP access in the IIJ4U web settings and use an app password if your account uses two-step verification.
Email domains using these settings
dd.iij4u.or.jp, ff.iij4u.or.jp, hh.iij4u.or.jp, kk.iij4u.or.jp, nn.iij4u.or.jp, pp.iij4u.or.jp, rr.iij4u.or.jp, ss.iij4u.or.jp, bc.iij4u.or.jp, bk.iij4u.or.jp, bp.iij4u.or.jp, bu.iij4u.or.jp.
Settings from the Mozilla Thunderbird ISP database (MPL 2.0), which mail clients use for automatic setup.
IIJ4U email settings: FAQ
What is the IIJ4U SMTP server?
Why does my IIJ4U login fail in a mail app?
Email validation API
Validate dd.iij4u.or.jp addresses before you send
emailvalidation.io checks syntax, MX records and the mailbox over SMTP, flags disposable, role and free addresses and returns a quality score, in one request.
Read the docs100 free validations every month. No credit card required.
GET https://api.emailvalidation.io/v1/info?email=name@dd.iij4u.or.jp
{
"email": "name@dd.iij4u.or.jp",
"domain": "dd.iij4u.or.jp",
"mx_found": true,
"smtp_check": …,
"free": …,
"disposable": false,
"state": "…"
}