Guide to PHP mb_send_mail: Preventing Garbled Text and Configuring Email Priority

mb_send_mail allows for multibyte-compatible email sending in PHP.
Issues like garbled characters or misrecognized headers often occur...

In such cases, or when using it in a Japanese environment, appropriate encoding and header settings are essential!
This article summarizes practical ways to use mb_send_mail and points to keep in mind.

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✅ Basic Usage

mb_language("Japanese");
mb_internal_encoding("UTF-8");

$to = "[e-mail]";
$subject = "Test Email";
$body = "This is a test email.";
$headers = "From: [e-mail]";

mb_send_mail($to, $subject, $body, $headers);

Why are mb_language and mb_internal_encoding necessary?

Function	Description
mb_language()	Performs MIME encoding for Japanese
mb_internal_encoding()	Specifies the internal character encoding used when encoding strings

Without these settings, the encoding for the subject and body will not be handled correctly, causing garbled characters...

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💡 Points for Header Settings

How to Write From, Cc, and Bcc

$headers = [];
$headers[] = 'From: Your Name <[e-mail]>';
$headers[] = 'Cc: [e-mail]';
$headers[] = 'Bcc: [e-mail]';

It's the same as common mailer software up to this point. 🙆‍♂️

To Set Priority

$headers[] = 'X-Priority: 1'; // Priority (1 is highest, 5 is lowest)
$headers[] = 'X-MSMail-Priority: High'; // For Outlook
$headers[] = 'Importance: High'; // General use

// Join header strings
$headerStr = implode("\r\n", $headers);

Pass this as the fourth argument of mb_send_mail.

What Can Be Configured?

I've put together a brief summary as a memo!

Check here if you're interested

Header Name	What does it do?	Additional Info	Commonly Used?
MIME-Version	Tells that the email is in MIME format	Normally fixed at "1.0"	△
Content-Transfer-Encoding	How to send the email content	"7bit" is fine for Japanese emails. base64 seems to get heavy.	△
Content-Type	Content type and character set	Use "text/plain;charset=UTF-8" etc. to prevent garbled characters	〇
Return-Path	Destination for error bounce emails	Usually added automatically by the server	〇
From	Who the email is from	Format like "Name <email address>" looks good	〇
Sender	Actual sender's address	Differences from From are technical, but think of it as for the sending program	〇
To	Recipient's email address	Separate multiple addresses with commas	〇
Cc	Others who should see it	Like a "Reference Copy." Same format as To	-
Bcc	Hidden recipients	Like a "Blind Copy." Also comma-separated	-
Reply-To	Reply-to email address	Usually defaults to From, but specify this if you want to change it	〇
Subject	Email subject	Passed as a separate argument in mb_send_mail, so no need in headers	×
Message-ID	ID to identify the email	Automatically generated, but can be set manually	-
Date	Sent date	Added automatically by the server	×
X-Priority	Email priority (1–5)	"1" is high, "5" is low priority. Used by Outlook, etc.	△
X-MSMail-Priority	Microsoft-specific priority	Specific setting for Outlook	-
Organization	Organization name (company, etc.)	Adding it might increase trust?	△
X-Mailer	Software used to send	Sometimes displayed by certain mailers	△
Precedence	Email category (list>junk>bulk)	Used for mass mailings etc.	-
Errors-To	Error reporting destination	Used in mailing lists, etc.	-

It seems there are many others...

This article by Ka2 (@ka215) on Qiita is very helpful for reference!
https://qiita.com/ka215/items/e5d21fe91a30fa968a2a

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📚 Summary

Here is the sample code from this article!

Sample Code

mb_language("Japanese");
mb_internal_encoding("UTF-8");

$to = "[e-mail]";
$subject = "[Important] Please check";
$body = "This is a multibyte-compatible test email.";

$headers = [];
$headers[] = 'From: Administrator <[e-mail]>';
$headers[] = 'Cc: [e-mail]';
$headers[] = 'Bcc: [e-mail]';
$headers[] = 'X-Priority: 1';
$headers[] = 'X-MSMail-Priority: High';
$headers[] = 'Importance: High';

$headerStr = implode("\r\n", $headers);

mb_send_mail($to, $subject, $body, $headerStr);

[Supplement] Check sendmail settings depending on the server
On shared or overseas servers, character garbling may occur due to the server's sendmail_path or MTA (such as Postfix) settings.

[Countermeasures]
Set default_charset = UTF-8 in php.ini.

When using the sendmail command, explicitly specify the envelope From with the -i or -f options.

Setting Item	Content
mb_language()	Enable MIME support for Japanese emails
mb_internal_encoding()	Set internal encoding for string operations
From/Cc/Bcc	Use appropriate encoded header formats
Priority	Add headers such as X-Priority and Importance
Header line break code	Use \r\n (Unix/Linux)

mb_send_mail is a convenient function, but using it incorrectly can lead to email delivery failures or character garbling. To ensure that emails are sent and displayed reliably, implement it with correct knowledge of headers and encoding!