parsePart() discards single-part multipart containers — body lost, treated as attachment

[gyoztes]

Description

When a multipart/alternative (or any multipart container) has only one sub-part (e.g. only text/html without a text/plain counterpart), the body is lost and misclassified as an attachment. getHTMLBody()
returns "", getTextBody() returns "".

This is common with transactional/automated emails (government portals, notification systems, etc.) that only send HTML without a text/plain alternative.

Root cause

In Structure.php, method parsePart(), line 118:

if (($boundary = $headers->getBoundary()) !== null) {
$parts = $this->detectParts($boundary, $body, $part_number);

  if(count($parts) > 1) {   // <-- BUG: should be > 0
      return $parts;
  }

}

return [new Part($body, $this->header->getConfig(), $headers, $part_number)];

When detectParts() finds exactly 1 sub-part inside the multipart container, count($parts) > 1 evaluates to false. The method falls through and wraps the entire raw multipart body as a single Part with
subtype=alternative.

isAttachment() then returns true for this part because "alternative" is not in the ["plain", "html"] whitelist (Part.php line 295), so the HTML content is never added to $this->bodies['html'] — it becomes a
ghost attachment instead.

Steps to reproduce

1. Receive an email with this MIME structure:
   Content-Type: multipart/mixed; boundary="outer"
   └── Content-Type: multipart/alternative; boundary="inner"
   └── Content-Type: text/html; charset="utf-8" ← only 1 sub-part, no text/plain
2. Fetch with php-imap
3. $message->getHTMLBody() returns "" (empty string)
4. $message->getAttachments() contains the HTML body as a fake attachment

Suggested fix

Change > 1 to > 0 in Structure.php:118:

if(count($parts) > 0) {
return $parts;
}

If detectParts() returns 0 parts, the existing fallthrough behavior is preserved. If it returns 1 or more, they are correctly returned as parsed sub-parts.

Environment

• php-imap version: 6.2.0
• PHP version: 8.4.18
• IMAP server: Microsoft 365 (Outlook)