WireMail::quotedPrintableString() causes some email clients to display encoded FROM name as plain text

[nurkka]

Short description of the issue

The WireMail core module builds the FROM header display name via:
WireMail::bundleEmailAndName() → WireMail::quotedPrintableString()
The method uses quoted_printable_encode() and wraps it as an RFC2047 encoded-word.

This can yield invalid encoded-words containing literal spaces (e.g. =?utf-8?Q?Firstname Lastname?=).
Some mail clients (confirmed in my case: eM Client) then display the raw encoded string in the sender field.

Steps to reproduce

$m = wireMail();
$m->to('recipient@example.com')
    ->from('sender@example.com', 'Firstname Lastname')
    ->subject('Test')
    ->body('Test')
    ->send();

Inspect raw headers:
FROM: may contain =?utf-8?Q?Firstname Lastname?=.

Expected

FROM header display name should be encoded so that it renders correctly in email clients (especially eM Client), which can only decode 100% valid RFC2047 (no spaces inside a single encoded-word).

Suggested fix

Replace quoted_printable_encode in WireMail::quotedPrintableString() with mb_encode_mimeheader() (mbstring):

public function quotedPrintableString($text) {  
    return mb_encode_mimeheader($text, 'UTF-8', 'Q', "\r\n");
}

This fix worked for me: eM Client now shows the FROM display name correctly.

File

wire/core/WireMail.php