Skip to content

User Guide

This document describes the management console provided by Customers Mail Cloud. The management console provides a web user interface for various settings and report references.

About notation

Describes the notation used in this document.

Service Plan

Depending on the service plan functions with different specifications give the following labels.

Pro Functions and descriptions with this label apply only to Pro plans.

Standard Functions and descriptions with this label apply only to Standard plans.


In the Pro plan, a subdomain of '' is assigned to each service user. In this document, the domain assigned to each service user is referred to as

Browsers supported by the management console

  • Google Chrome
  • Mozilla Firefox
  • Microsoft Edge based on Chromium


Customers Mail Cloud provides the functions required for the application such as sending an email and referencing the email address that caused the sending error with the API.

Users for accessing the API (API users) are created and managed in the management console. Perform the API operation settings.

Email Sending API

We provide single-send or bulk-send email API.

Transaction Email API

This API allows you to handle event datas that are used by SMTP and Email Sending API.

Sender Authentication

Perform the sender authentication settings provided by Customers Mail Cloud.


Customers Mail Cloud provides the ability to add a DKIM signature to emails sent via SMTP or API. Create a DKIM key by registering the sender domain (header From domain) in the management console. You can send a DKIM-signed emails by publishing this to the service user's DNS.


You can start using SPF by publishing the SPF record provided by Customers Mail Cloud to the DNS of the service user.


Customers Mail Cloud provides a function that can add S/MIME signatures to emails sent via mail relay or API.

DMARC (only in Japanese)

Using mail sending authentication, Customers Mail Cloud provides the mail sender with the policy and reports.


You can view various reports from the management console.

Error Log

You can search and refer to the e-mail address that has the delivery error. Customers Mail Cloud analyzes SMTP errors and bounce emails and classifies them into Error Status such as Unknown User, Unknown Host, etc. This allows you to check the reason for the delivery error.

Error Graph

Shows the error status in a pie chart. You can visually check why the delivery error is occurring. Since you can see the error status for each domain, you can search the cause of delivery errors occurring in a specific domain.

Delivery Log

You can search and refer the sending status of each email. You can quickly search the status of that email when you receive an inquiry such as an email not being delivered. Customers Mail Cloud manages the sending status of emails with four delivery statuses.

Delivery Graph

Shows the delivery status email traffic in a line graph. You can visually check how much email traffic has occured and what the situation is.

Delivery Domain

Shows which domain (ISP) has the most mail sending in a pie chart. You can analyze destination domains and optimize email delivery control, such as adjusting delivery speed settings for domains with heavy email traffic.

Delivery statistics

You can see the number of daily mail deliveries in a table format.

Report retention period

A retention period is provided for data that can be referenced in delivery reports, such as delivery logs and error logs. Report data that retention period has expired will be deleted on a daily basis. The retention period for report data is 40 days.


Various setting operations of Customers Mail Cloud is performed.

Relay Server

Performs various settings for connecting SMTP and the mail relay server.

You can set the number of simultaneous connections, reception interval, reception size, connection IP, etc.

Receiving Server

You can perform settings to receive the incoming emails by using the Inbound Webhook and bounce emails.

Email Forwarding

You can send a copy of the email that matches the filter to the forwarding email address, or you can rewrite the destination address to the forwarding email address and send it.

For example, you can copy an email sent by the system, such as purchase confirmation email, and save and refer to it at the forwarding email address.

Delivery Blocking

It provides a function that automatically suppress sending emails to email addresses whose users are unknown. Mobile carriers and major ISPs prohibit sending a large amount of e-mail to an e-mail address with unknown user as a junk e-mail act. By enabling this function, email addresses that have become unknown user are automatically cleaned, and highly reachable email delivery can be achieved.

Delivery Speed

Perform settings to send mail at the optimum speed and define the number of simultaneous connections for each destination domain, delivery interval, and transmission IP number. You can also perform forwarding settings to forward a specific domain to another mail server.

Delivery Priority

You can specify any mail header and set which mail should be preferentially delivered. Delay issues caused by campaign emails can be solve to prioritise emails of importance such as document request confirmation.

Delivery Prohibited Time Zone

You can specify any email header and set the time zone when email delivery is prohibited. You can control not to send emails other than the specified time zone.Such as campaign mails that are not desirable receiving during night.

Advanced Settings

You can perform controls such as deleting the received header given by the application or Postfix, controlling the resend period and resend interval of the email that has a temporary error, and rewrite the envelope From to send the bounce email to the specified domain.

One-click Unsubscribe

By using the "List-Unsubscribe" feature, you will be able to "send out emails with a List-unsubsciribe header added" and "list email recipients who have clicked on the unsubscribe link" on the Customers Mail Cloud.


Performs various management of the management console.


Create and manage an account to log in to the management console. You can give authorization to accounts such as "Service Administrator" who can change various settings and "Report Viewer" who can only view reports.

Connection IP

IP-based access control can be performed by registering the IP address that can access to management console and API.

Operation Log

You can check the operation of the management console and the login record.

My Account

You can change the password, language, and time zone of the logged-in account.

In addition to the above, group administrators can set up two-factor authentication and reissue OTP keys.

Common specifications

This section describes the specifications that are common to the various functions of the management console.

TLS version

Https over TLS 1.2 is applied when you access to the management console.

Mail Address

E-mail addresses are defined in the E-mail specifications RFC 5321 and RFC 5322, but in reality, e-mail addresses that are not defined are also used. In this service you can extend the email address defined in RFC and use the commonly used format. The email address formats that can be used are as follows.

The email address is in the form of "localpart@domain part". This local part and the domain part will explained separately.

Local Part

  • Characters that can be used for the local part are alphanumeric characters and some symbols "! # $ % & ' * + - / = ? ^ \ _ ` { | } ~"
  • In addition, you can use "." Other than the beginning. (Consecutive "." cannot be used in specifications, but it is enabled by applying the exception of the local part described later.)

Domain Part

  • The characters that can be used for the domain part are alphanumeric characters and "." "-" "_".
  • However, "." cannot be used at the beginning or end.
  • Also, consecutive "." cannot be used.
  • Each character string separated by "." must start with alphanumeric characters.
Local Part Exception
  • If the local part contains characters that cannot be used, you can use them by enclosing them in " " as long as they are within the range of us-ascii.
  • When enclosed in " ", " is converted to "\"" and "\" is converted to "\\".
  • If you can use a local part that not enclosed in " " , it is internally enclosed in " " and accepted. (Wrap up when sending an email)
Examples that can be used by enclosing them in " "
Contains characters that cannot be used Can be used by enclosing it in "" Description "irregular..pattern" Example of continuous "."
hello\(^^) "hello\\(^^)" Example of escape "\"
Domain Part "_"

Due to the specifications, "_" cannot be used for domain names. However, since it can be set in DNS, there are cases where subdomains and host names including "_" are operated. Therefore, "_" can be used in this system.

Length of the Mail Address

The email address is up to 256 bytes according to the rules of SMTP. However, in reality, an email addresses higher than that are used. The length of email address is not checked, but since it is limited to 1000 bytes per line according to the rules of SMTP, the RCPT TO command must fit in this length.

Email address comparison

The comparison of e-mail addresses when searching for or registering e-mail addresses on this system is not case sensitive.


Even "" is "Who@Exmple.Com", treat as the same email address.


In the management console, operating conditions can be set by combining mail headers and values. This operating condition is called a filter.

Header Name

If "To" is specified for the header name, the value of envelope-to is evaluated. For the header name, 'From', 'Subject', and the extended mail header (X-priority, etc.) given by the application can be specified. Header names are matched, ignoring case.


Multiple mail headers such as 'Received' cannot be specified in the operating conditions.

Header Value

For the header value, specify a regex to evaluate the value. For example, if you want to match the domain part of To (envelope-to), write .+@Example\.com. If you want to specify a full match of the email address including the local part, write user-name@example\.com.


If you want to specify From as the header name and match the email address,

Write .*user-name@example\.com.

In some cases, the header value is "name" <email address> and a character string is added before and after the email address.

The syntax of a typical regex is explained below.For all available syntax please reder to Java Pattern

syntax Description
x character x
\ Backslash character
. Any single character (If you want to express a dot, You need to escape it with "\".)
X? X 1 or 0 times
X* X more than 0
X+ X more than 1
X{n} X n times
X{n,} X more than n
X{n,m} X more than n less than m
[abc] a,b,or,c
[^abc] Characters other than a,b,c
[a-zA-Z] a-z, A-Z (range)

Delivery Status

Customers Mail Cloud records the status of each email in four 'status'. This status is called delivery status. The delivery status is displayed in the delivery graph and delivery log. Also, specify it as a request parameter when acquiring delivery data with the API.

Status Description
queued Email was received from the mail relay source server.
succeeded SMTP communication was successful and mail sent to the destination server.
failed SMTP communication failed and mail could not be sent to the destination server.
deferred The mail is being resent because there was a temporary error response from the destination server.

If the error log appears in spite of the mail has a status "succeeded"

Some mails are appeared in the error log after these mails have "succeeded" status. This means finally failed delivery. Sending the mail from Customers Mail Cloud is succeeded, but the situation is that the bounce mail is returned from the received mail server later.

In that case, you should confirm the reason in the error log and ask the administrator of the received mail server about that situation.

Error Status

If an error occurs when sending an email, parse the SMTP reply message or bounce email and records the status defined by Customers Mail Cloud. This is called the error status.The error status is displayed in the error graph and error log. Also, specify it as a request parameter when acquiring transmission error data with the API.

Error status Error reason Cause
1 Unkown host The host could not be resolved by DNS.
2 Unkown user Maill address does not exist.
3 Resend timeout Resending was performed but was not completed in time because the destination server could not be connected or a temporary error response was returned.
4 Receipt rejection Mail reception was rejected due to the policy of the destination server.
5 Over capacity The destination server was unable to receive mail because it exceeded the mailbox capacity or mail server disk space limits.
6 Forwarding error Failed to send an email to an address different from the destination address you sent. After you save the mail to the destination address in the recipient's settings and then forward it to another address, the mail may have arrived at the destination address.
7 Receiving server error Delivery failed due to a misconfiguration of the destination server (SMTP authentication is set on port 25, the destination e-mail address is not managed even though the host is resolved by DNS and connected).
8 Oversize The destination server rreject to receive because the mail size was too large.
9 Address format error The destination email address does not follow the email address format.
10 Blocked address Suppressed emails sending with the blocking function.
11 Unsubscribed address Suppressed emails sending with the One-click Unsubscrbe function.
99 Other erros Email sending failed because the destination server responded with a permanent error.

About Customers Mail Cloud

Describes the service outline of Customers Mail Cloud. (Available only in Japanese)

Getting Started

This is a summary of the settings required from the time you get an account to the start using the service. Please see this document first. (Available only in Japanese)

API Reference

Explains how to use the API and interface specifications. Please see this document for more information about API.

System Integration

Explains specific know-how for system linkage with Customers Mail Cloud and how to connect existing applications such as Postfix, Java, PHP, Python with SMTP interface. (Available only in Japanese)