PHP – Encode string for MIME header using mb_encode_mimeheader()

In PHP, mb_encode_mimeheader() function is used to encode a string for MIME (Multipurpose Internet Mail Extensions) header. It encodes a given string by the MIME header encoding scheme, which is essential for email headers containing non-ASCII characters.

Syntax

string mb_encode_mimeheader(
    string $string,
    ?string $charset = null,
    ?string $transfer_encoding = null,
    string $newLine = "\r<br>",
    int $indent = 0
)

Parameters

The mb_encode_mimeheader() function accepts five parameters −

• $string − The string to encode. Its encoding should be the same as mb_internal_encoding()

• $charset − The character set name in which the string is represented (optional, defaults to internal encoding)

• $transfer_encoding − The MIME encoding scheme. Should be "B" (base64) or "Q" (Quoted-printable). Defaults to "B"

• $newLine − The end-of-line (EOL) marker for line-folding (defaults to "\r
  ")

• $indent − Indentation of the first line (defaults to 0)

Return Value

Returns a converted version of the string that is represented in ASCII format suitable for MIME headers.

Example 1: Basic Email Header Encoding

Here's how to encode a string for an email header ?

<?php
   $name = "Online tutorials";
   $mbox = "user";
   $domain = "example.com";
   $addr = mb_encode_mimeheader($name, "UTF-8", "Q") . " <" . $mbox . "@" . $domain . ">";
   echo $addr;
?>

Online tutorials <user@example.com>

Example 2: Encoding Unicode Characters

This example shows how to encode special Unicode characters ?

<?php
   $string = "?";  // Arrow symbol
   mb_internal_encoding("UTF-8");
   echo mb_encode_mimeheader($string, 'UTF-8', 'B');
?>

=?UTF-8?B?4oaS?=

Example 3: Comparing Encoding Methods

Let's compare Base64 (B) and Quoted-Printable (Q) encoding ?

<?php
   $subject = "Café Newsletter";
   
   echo "Base64 (B): " . mb_encode_mimeheader($subject, 'UTF-8', 'B') . "<br>";
   echo "Quoted-Printable (Q): " . mb_encode_mimeheader($subject, 'UTF-8', 'Q');
?>

Base64 (B): =?UTF-8?B?Q2Fmw6kgTmV3c2xldHRlcg==?=
Quoted-Printable (Q): =?UTF-8?Q?Caf=C3=A9_Newsletter?=

Common Use Cases

• Email Subject Lines − Encoding non-ASCII characters in email subjects

• From/To Headers − Encoding names in email addresses

• Custom Headers − Any email header containing special characters

Conclusion

The mb_encode_mimeheader() function is essential for properly encoding email headers with non-ASCII characters. Use Base64 encoding for binary data and Quoted-Printable for mostly ASCII text with occasional special characters.