diff --git a/README.md b/README.md
index 99aaf4de..19e05425 100644
--- a/README.md
+++ b/README.md
@@ -144,6 +144,10 @@ if($mail->hasAttachments()) {
 // Print all information of $mail
 print_r($mail);
 
+// Access arbitrary headers without adding custom properties to the library
+$originMessageId = $mail->getHeader('Origin-MessageID');
+$receivedHeaders = $mail->getHeaders('Received');
+
 // Print all attachements of $mail
 echo "\n\nAttachments:\n";
 print_r($mail->getAttachments());
diff --git a/src/PhpImap/IncomingMailHeader.php b/src/PhpImap/IncomingMailHeader.php
index 7e522b6f..8351a2d8 100644
--- a/src/PhpImap/IncomingMailHeader.php
+++ b/src/PhpImap/IncomingMailHeader.php
@@ -44,6 +44,13 @@ class IncomingMailHeader
     /** @var string|null */
     public $headersRaw;
 
+    /**
+     * @var string[][]
+     *
+     * @psalm-var array<string, list<string>>
+     */
+    public $headersByName = [];
+
     /** @var object|null */
     public $headers;
 
@@ -152,4 +159,134 @@ class IncomingMailHeader
 
     /** @var string|null */
     public $references;
+
+    public function setHeadersRaw(string $headersRaw): void
+    {
+        $this->headersRaw = $headersRaw;
+        $this->headersByName = $this->parseHeadersRaw($headersRaw);
+    }
+
+    public function getHeader(string $headerName): ?string
+    {
+        $headers = $this->getHeaders($headerName);
+
+        if ([] === $headers) {
+            return null;
+        }
+
+        return $headers[0];
+    }
+
+    /**
+     * @return string[]
+     *
+     * @psalm-return list<string>
+     */
+    public function getHeaders(string $headerName): array
+    {
+        $this->ensureParsedHeadersByName();
+
+        return $this->headersByName[$this->normalizeHeaderName($headerName)] ?? [];
+    }
+
+    /**
+     * @return string[][]
+     *
+     * @psalm-return array<string, list<string>>
+     */
+    public function getAllHeaders(): array
+    {
+        $this->ensureParsedHeadersByName();
+
+        return $this->headersByName;
+    }
+
+    protected function ensureParsedHeadersByName(): void
+    {
+        if ([] !== $this->headersByName || null === $this->headersRaw) {
+            return;
+        }
+
+        $this->headersByName = $this->parseHeadersRaw($this->headersRaw);
+    }
+
+    /**
+     * @return string[][]
+     *
+     * @psalm-return array<string, list<string>>
+     */
+    protected function parseHeadersRaw(string $headersRaw): array
+    {
+        $parsedHeaders = [];
+        $currentHeaderName = null;
+        $currentHeaderValue = '';
+
+        foreach ($this->splitHeaderLines($headersRaw) as $line) {
+            if ('' === $line) {
+                $this->storeParsedHeader($parsedHeaders, $currentHeaderName, $currentHeaderValue);
+                $currentHeaderName = null;
+                $currentHeaderValue = '';
+
+                continue;
+            }
+
+            if (null !== $currentHeaderName && 1 === \preg_match('/^[ \t]/', $line)) {
+                $currentHeaderValue .= ' '.\ltrim($line);
+
+                continue;
+            }
+
+            $this->storeParsedHeader($parsedHeaders, $currentHeaderName, $currentHeaderValue);
+
+            $separatorPosition = \strpos($line, ':');
+
+            if (false === $separatorPosition) {
+                $currentHeaderName = null;
+                $currentHeaderValue = '';
+
+                continue;
+            }
+
+            $currentHeaderName = \substr($line, 0, $separatorPosition);
+            $currentHeaderValue = \trim(\substr($line, $separatorPosition + 1));
+        }
+
+        $this->storeParsedHeader($parsedHeaders, $currentHeaderName, $currentHeaderValue);
+
+        return $parsedHeaders;
+    }
+
+    /**
+     * @return string[]
+     *
+     * @psalm-return list<string>
+     */
+    protected function splitHeaderLines(string $headersRaw): array
+    {
+        /** @var list<string> */
+        return \explode("\n", \str_replace(["\r\n", "\r"], "\n", $headersRaw));
+    }
+
+    /**
+     * @param string[][]  $parsedHeaders
+     * @param string|null $headerName
+     *
+     * @psalm-param array<string, list<string>> $parsedHeaders
+     */
+    protected function storeParsedHeader(array &$parsedHeaders, ?string $headerName, string $headerValue): void
+    {
+        if (null === $headerName || '' === \trim($headerName)) {
+            return;
+        }
+
+        $headerName = $this->normalizeHeaderName($headerName);
+
+        $parsedHeaders[$headerName] ??= [];
+        $parsedHeaders[$headerName][] = \trim($headerValue);
+    }
+
+    protected function normalizeHeaderName(string $headerName): string
+    {
+        return \strtolower(\trim($headerName));
+    }
 }
diff --git a/src/PhpImap/Mailbox.php b/src/PhpImap/Mailbox.php
index b621aa92..d6e2514c 100644
--- a/src/PhpImap/Mailbox.php
+++ b/src/PhpImap/Mailbox.php
@@ -1290,7 +1290,7 @@ public function getMailHeader(int $mailId): IncomingMailHeader
         }
 
         $header = new IncomingMailHeader();
-        $header->headersRaw = $headersRaw;
+        $header->setHeadersRaw($headersRaw);
         $header->headers = $head;
         $header->id = $mailId;
         $header->imapPath = $this->imapPath;
diff --git a/tests/unit/IncomingMailHeaderTest.php b/tests/unit/IncomingMailHeaderTest.php
new file mode 100644
index 00000000..d81001ab
--- /dev/null
+++ b/tests/unit/IncomingMailHeaderTest.php
@@ -0,0 +1,69 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpImap;
+
+use PHPUnit\Framework\TestCase;
+
+final class IncomingMailHeaderTest extends TestCase
+{
+    public function testSetHeadersRawParsesFoldedRepeatedAndCaseInsensitiveHeaders(): void
+    {
+        $header = new IncomingMailHeader();
+        $header->setHeadersRaw(
+            "Origin-MessageID: <origin@example.com>\r\n".
+            "X-Trace: first\r\n".
+            "\tcontinued\r\n".
+            "x-trace: second\r\n".
+            "Subject: Example\r\n"
+        );
+
+        $this->assertSame('<origin@example.com>', $header->getHeader('origin-messageid'));
+        $this->assertSame(
+            ['first continued', 'second'],
+            $header->getHeaders('X-TRACE')
+        );
+        $this->assertSame(
+            [
+                'origin-messageid' => ['<origin@example.com>'],
+                'x-trace' => ['first continued', 'second'],
+                'subject' => ['Example'],
+            ],
+            $header->getAllHeaders()
+        );
+    }
+
+    public function testGetHeaderLazilyParsesDirectlyAssignedHeadersRaw(): void
+    {
+        $header = new IncomingMailHeader();
+        $header->headersRaw = "X-Custom-Header: custom value\r\n";
+
+        $this->assertSame('custom value', $header->getHeader('x-custom-header'));
+        $this->assertSame(
+            ['custom value'],
+            $header->headersByName['x-custom-header']
+        );
+        $this->assertNull($header->getHeader('missing-header'));
+        $this->assertSame([], $header->getHeaders('missing-header'));
+    }
+
+    public function testIncomingMailRetainsParsedHeadersAfterSetHeader(): void
+    {
+        $header = new IncomingMailHeader();
+        $header->setHeadersRaw(
+            "X-Custom-Header: custom value\r\n".
+            "Received: mx1.example.test\r\n".
+            "Received: mx2.example.test\r\n"
+        );
+
+        $mail = new IncomingMail();
+        $mail->setHeader($header);
+
+        $this->assertSame('custom value', $mail->getHeader('X-Custom-Header'));
+        $this->assertSame(
+            ['mx1.example.test', 'mx2.example.test'],
+            $mail->getHeaders('received')
+        );
+    }
+}