diff --git a/bin/sentry-agent b/bin/sentry-agent
index 60b83a4..0e477e2 100755
--- a/bin/sentry-agent
+++ b/bin/sentry-agent
@@ -63,7 +63,13 @@ $queue = new EnvelopeQueue(
     $upstreamConcurrency,
     $queueLimit,
     function (Envelope $envelope) use ($forwarder) {
-        return $forwarder->forward($envelope);
+        try {
+            return $forwarder->forward($envelope);
+        } catch (Exception $e) {
+            Log::error("Failed to forward envelope: {$e->getMessage()}");
+
+            return new React\Promise\Internal\RejectedPromise($e);
+        }
     }
 );
 
diff --git a/composer.json b/composer.json
index 2cad05e..982f9b2 100644
--- a/composer.json
+++ b/composer.json
@@ -12,6 +12,7 @@
     ],
     "require": {
         "php": "^7.2|^8",
+        "ext-json": "*",
         "clue/mq-react": "^1.6",
         "react/http": "^1.11",
         "react/socket": "^1.16",
@@ -24,7 +25,13 @@
     },
     "require-dev": {
         "friendsofphp/php-cs-fixer": "^3.70",
-        "phpstan/phpstan": "^2.1"
+        "phpstan/phpstan": "^2.1",
+        "phpunit/phpunit": "^8.5|^9.6"
+    },
+    "autoload-dev": {
+        "psr-4": {
+            "Sentry\\Agent\\Tests\\": "tests/"
+        }
     },
     "bin": [
         "bin/sentry-agent"
@@ -32,8 +39,10 @@
     "scripts": {
         "check": [
             "@cs-check",
-            "@phpstan"
+            "@phpstan",
+            "@tests"
         ],
+        "tests": "vendor/bin/phpunit --verbose",
         "cs-check": "vendor/bin/php-cs-fixer fix --verbose --diff --dry-run",
         "cs-fix": "vendor/bin/php-cs-fixer fix --verbose --diff",
         "phpstan": "vendor/bin/phpstan analyse"
diff --git a/phpunit.xml b/phpunit.xml
new file mode 100644
index 0000000..263d883
--- /dev/null
+++ b/phpunit.xml
@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
+         backupGlobals="true"
+         colors="true"
+         bootstrap="vendor/autoload.php"
+         cacheResult="false"
+         beStrictAboutOutputDuringTests="true"
+>
+    <testsuites>
+        <testsuite name="unit">
+            <directory>tests</directory>
+        </testsuite>
+    </testsuites>
+
+    <coverage>
+        <include>
+            <directory suffix=".php">src</directory>
+        </include>
+    </coverage>
+</phpunit>
diff --git a/src/Envelope.php b/src/Envelope.php
index a80af1f..1082f6b 100644
--- a/src/Envelope.php
+++ b/src/Envelope.php
@@ -4,51 +4,182 @@
 
 namespace Sentry\Agent;
 
+use Sentry\Agent\Exceptions\MalformedEnvelope;
+use Sentry\Dsn;
+
 /**
  * @internal
+ *
+ * @phpstan-type EnvelopeHeader array{
+ *     dsn: string,
+ * }
  */
 class Envelope
 {
+    public const CONTENT_TYPE = 'application/x-sentry-envelope';
+
+    /**
+     * @var EnvelopeHeader The envelope header
+     */
+    private $header;
+
     /**
-     * @var string
+     * @var EnvelopeItem[] The envelope items
      */
-    private $data;
+    private $items;
 
-    public function __construct(string $data)
+    /**
+     * @param EnvelopeHeader $header
+     * @param EnvelopeItem[] $items
+     */
+    public function __construct(array $header, array $items)
     {
-        $this->data = $data;
+        $this->header = $header;
+        $this->items = $items;
     }
 
-    public function getDsn(): ?string
+    /**
+     * @return EnvelopeHeader
+     */
+    public function getHeader(): array
     {
-        $header = $this->getHeader();
-
-        if ($header === null) {
-            return null;
-        }
+        return $this->header;
+    }
 
-        $parsedHeader = json_decode($header, true);
+    public function getDsn(): Dsn
+    {
+        return Dsn::createFromString($this->header['dsn']);
+    }
 
-        if (\is_array($parsedHeader) && !empty($parsedHeader['dsn']) && \is_string($parsedHeader['dsn'])) {
-            return $parsedHeader['dsn'];
-        }
+    /**
+     * @return EnvelopeItem[]
+     */
+    public function getItems(): array
+    {
+        return $this->items;
+    }
 
-        return null;
+    /**
+     * @param callable(EnvelopeItem): bool $callback if the callback returns true, the item will be removed from the envelope
+     */
+    public function rejectItems(callable $callback): void
+    {
+        $this->items = array_filter(
+            $this->items,
+            static function (EnvelopeItem $item) use ($callback) {
+                return !$callback($item);
+            }
+        );
     }
 
-    public function getData(): string
+    public function __toString()
     {
-        return $this->data;
+        $data = implode(
+            "\n",
+            array_map(
+                static function (EnvelopeItem $item): string {
+                    return (string) $item;
+                }, $this->items
+            )
+        );
+
+        // We always terminate with an additional newline
+        return json_encode($this->header) . "\n{$data}";
     }
 
-    public function getHeader(): ?string
+    /**
+     * @throws MalformedEnvelope
+     */
+    public static function fromString(string $envelope): self
     {
-        $position = strpos($this->data, "\n");
+        $consumePart = static function () use (&$envelope): ?string {
+            // Once we fully consumed the envelope, we return null indicating EOF
+            if ($envelope === '') {
+                return null;
+            }
+
+            // Parts are newline delimited so we can find the next newline to find the end of the next part
+            $nextNewline = strpos($envelope, "\n");
+
+            if ($nextNewline === false) {
+                $nextNewline = \strlen($envelope);
+            }
+
+            $part = substr($envelope, 0, $nextNewline);
+
+            // We consume the newline as well
+            $envelope = substr($envelope, $nextNewline + 1);
+
+            // Empty parts are additional trailing newlines, which can be ignored
+            if ($part === '') {
+                return null;
+            }
+
+            return $part;
+        };
+
+        $consumeBytes = static function (int $bytes) use (&$envelope): string {
+            if (\strlen($envelope) < $bytes) {
+                throw new MalformedEnvelope('Envelope reached EOF before consuming expected bytes');
+            }
+
+            $part = substr($envelope, 0, $bytes);
+
+            $envelope = substr($envelope, $bytes + 1);
+
+            return $part;
+        };
+
+        $parseJson = static function (?string $json): array {
+            if ($json === null) {
+                throw new MalformedEnvelope('Envelope reached EOF before consuming expected JSON');
+            }
+
+            $decoded = json_decode($json, true);
+
+            if (!\is_array($decoded)) {
+                // Technically we could have a non-JSON error here (if we try to parse a single JSON scalar for example)
+                // but we don't really care if that happens and we can just assume there was a problem parsing the JSON if we don't get an array
+                throw new MalformedEnvelope('Failed to decode JSON: ' . json_last_error_msg());
+            }
+
+            return $decoded;
+        };
+
+        // The first part is always the envelope header
+        $header = $parseJson($consumePart());
+
+        // Technically the header could not contain the DSN key, but we don't really care about that case since we won't be able to forward the envelope
+        if (!isset($header['dsn'])) {
+            throw new MalformedEnvelope('Envelope header does not contain a DSN');
+        }
+
+        $items = [];
+
+        while ($rawItemHeader = $consumePart()) {
+            $itemHeader = $parseJson($rawItemHeader);
+
+            // The item header should always contain the type
+            if (!isset($itemHeader['type'])) {
+                throw new MalformedEnvelope('Envelope item header does not contain a type');
+            }
+
+            // The size in the header is optional
+            $itemContentLength = $itemHeader['length'] ?? null;
+
+            if ($itemContentLength === null) {
+                $itemContent = $consumePart();
+
+                if ($itemContent === null) {
+                    throw new MalformedEnvelope('Envelope reached EOF before consuming expected item content');
+                }
+            } else {
+                $itemContent = $consumeBytes($itemContentLength);
+            }
 
-        if ($position === false) {
-            return null;
+            $items[] = new EnvelopeItem($itemHeader, $itemContent);
         }
 
-        return substr($this->data, 0, $position);
+        return new self($header, $items);
     }
 }
diff --git a/src/EnvelopeForwarder.php b/src/EnvelopeForwarder.php
index ca9260a..d8a4a7c 100644
--- a/src/EnvelopeForwarder.php
+++ b/src/EnvelopeForwarder.php
@@ -8,6 +8,8 @@
 use React\Http\Browser;
 use React\Promise\PromiseInterface;
 use Sentry\Dsn;
+use Sentry\HttpClient\Response;
+use Sentry\Transport\RateLimiter;
 
 /**
  * @internal
@@ -44,6 +46,11 @@ class EnvelopeForwarder
      */
     private $onEnvelopeError;
 
+    /**
+     * @var array<string, RateLimiter>
+     */
+    private $rateLimiters = [];
+
     /**
      * @param callable(ResponseInterface): void $onEnvelopeSent  called when the envelope is sent
      * @param callable(\Throwable): void        $onEnvelopeError called when the envelope fails to send
@@ -62,11 +69,20 @@ public function forward(Envelope $envelope): PromiseInterface
     {
         $dsn = $envelope->getDsn();
 
-        if ($dsn === null) {
-            throw new \RuntimeException('The envelope does not contain a DSN.');
-        }
+        $rateLimiter = $this->getRateLimiter($dsn);
+
+        $envelope->rejectItems(static function (EnvelopeItem $envelopeItem) use ($rateLimiter) {
+            $envelopeItemType = $envelopeItem->getItemType();
+
+            // @TODO: We should make the rate limiter accept an arbitrary item type to allow for flexibility when adding new item types
+            if ($envelopeItemType === null) {
+                return false;
+            }
+
+            return $rateLimiter->isRateLimited($envelopeItemType);
+        });
 
-        $dsn = Dsn::createFromString($dsn);
+        // @TODO: If we rate limit all the items we have an empty envelope which we should not send and just return
 
         $authHeader = [
             'sentry_version=' . self::PROTOCOL_VERSION,
@@ -76,10 +92,32 @@ public function forward(Envelope $envelope): PromiseInterface
 
         // @TODO: Implement any number of missing options like the user-agent, encoding, proxy etc.
 
-        return (new Browser())->withTimeout($this->timeout)->post($dsn->getEnvelopeApiEndpointUrl(), [
-            'User-Agent' => self::IDENTIFIER . '/' . self::VERSION,
-            'Content-Type' => 'application/x-sentry-envelope',
-            'X-Sentry-Auth' => 'Sentry ' . implode(', ', $authHeader),
-        ], $envelope->getData())->then($this->onEnvelopeSent, $this->onEnvelopeError);
+        // @TODO: We might want to replace this Browser API with a cURL implementation using curl_multi_exec
+        return (new Browser())->withTimeout($this->timeout)->post(
+            $dsn->getEnvelopeApiEndpointUrl(),
+            [
+                'User-Agent' => self::IDENTIFIER . '/' . self::VERSION,
+                'Content-Type' => Envelope::CONTENT_TYPE,
+                'X-Sentry-Auth' => 'Sentry ' . implode(', ', $authHeader),
+            ],
+            (string) $envelope
+        )->then(function (ResponseInterface $response) use ($rateLimiter) {
+            $rateLimiter->handleResponse(
+                new Response($response->getStatusCode(), $response->getHeaders(), $response->getStatusCode() > 400 ? $response->getBody()->getContents() : '')
+            );
+
+            \call_user_func($this->onEnvelopeSent, $response);
+        }, $this->onEnvelopeError);
+    }
+
+    private function getRateLimiter(Dsn $dsn): RateLimiter
+    {
+        $key = $dsn->getEnvelopeApiEndpointUrl();
+
+        if (!isset($this->rateLimiters[$key])) {
+            $this->rateLimiters[$key] = new RateLimiter();
+        }
+
+        return $this->rateLimiters[$key];
     }
 }
diff --git a/src/EnvelopeItem.php b/src/EnvelopeItem.php
new file mode 100644
index 0000000..4a4a6d4
--- /dev/null
+++ b/src/EnvelopeItem.php
@@ -0,0 +1,69 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sentry\Agent;
+
+use Sentry\EventType;
+
+/**
+ * @internal
+ *
+ * @phpstan-type EnvelopeItemHeader array{
+ *     type: string,
+ * }
+ */
+class EnvelopeItem
+{
+    /**
+     * @var EnvelopeItemHeader The envelope item header
+     */
+    private $header;
+
+    /**
+     * @var string The envelope item data
+     */
+    private $data;
+
+    /**
+     * @param EnvelopeItemHeader $header The envelope item header
+     * @param string             $data   The envelope item data
+     */
+    public function __construct(array $header, string $data)
+    {
+        $this->header = $header;
+        $this->data = $data;
+    }
+
+    /**
+     * @return EnvelopeItemHeader
+     */
+    public function getHeader(): array
+    {
+        return $this->header;
+    }
+
+    public function getItemType(): ?EventType
+    {
+        switch ($this->header['type']) {
+            case (string) EventType::event():
+                return EventType::event();
+            case (string) EventType::transaction():
+                return EventType::transaction();
+            case (string) EventType::checkIn():
+                return EventType::checkIn();
+            default:
+                return null;
+        }
+    }
+
+    public function getData(): string
+    {
+        return $this->data;
+    }
+
+    public function __toString()
+    {
+        return json_encode($this->header) . "\n" . $this->data;
+    }
+}
diff --git a/src/Exceptions/MalformedEnvelope.php b/src/Exceptions/MalformedEnvelope.php
new file mode 100644
index 0000000..2dcf03c
--- /dev/null
+++ b/src/Exceptions/MalformedEnvelope.php
@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sentry\Agent\Exceptions;
+
+class MalformedEnvelope extends \RuntimeException
+{
+}
diff --git a/src/Server.php b/src/Server.php
index e544fb6..d77b041 100644
--- a/src/Server.php
+++ b/src/Server.php
@@ -6,6 +6,7 @@
 
 use React\Socket\ConnectionInterface;
 use React\Socket\SocketServer;
+use Sentry\Agent\Exceptions\MalformedEnvelope;
 
 /**
  * @internal
@@ -76,7 +77,11 @@ public function run(): void
                         break;
                     }
 
-                    \call_user_func($this->onEnvelopeReceived, new Envelope(substr($connectionBuffer, 4, $messageLength)));
+                    try {
+                        \call_user_func($this->onEnvelopeReceived, Envelope::fromString(substr($connectionBuffer, 4, $messageLength)));
+                    } catch (MalformedEnvelope $e) {
+                        \call_user_func($this->onConnectionError, $e);
+                    }
 
                     $connectionBuffer = substr($connectionBuffer, $messageLength);
                     $messageLength = 0;
diff --git a/tests/EnvelopeTest.php b/tests/EnvelopeTest.php
new file mode 100644
index 0000000..92daf53
--- /dev/null
+++ b/tests/EnvelopeTest.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sentry\Agent\Tests;
+
+use PHPUnit\Framework\TestCase;
+use Sentry\Agent\Envelope;
+
+class EnvelopeTest extends TestCase
+{
+    public function testCanParsePhpSdkExampleEvent(): void
+    {
+        $payload = $this->getFixture('envelope_with_php_sdk_event');
+
+        $envelope = Envelope::fromString($payload);
+
+        $this->assertCount(1, $envelope->getItems());
+
+        $this->assertEquals('event', $envelope->getItems()[0]->getHeader()['type']);
+
+        $this->assertEquals($payload, (string) $envelope);
+    }
+
+    public function testCanParseLogsExampleEvent(): void
+    {
+        $payload = $this->getFixture('envelope_with_log_item');
+
+        $envelope = Envelope::fromString($payload);
+
+        $this->assertCount(1, $envelope->getItems());
+
+        $this->assertEquals('log', $envelope->getItems()[0]->getHeader()['type']);
+
+        $this->assertEquals($payload, (string) $envelope);
+    }
+
+    public function testCanParseEnvelopeWith2Items(): void
+    {
+        $payload = $this->getFixture('envelope_with_2_items');
+
+        $envelope = Envelope::fromString($payload);
+
+        $this->assertEquals('https://e12d836b15bb49d7bbf99e64295d995b:@sentry.io/42', $envelope->getHeader()['dsn']);
+
+        $this->assertCount(2, $envelope->getItems());
+
+        $this->assertEquals('attachment', $envelope->getItems()[0]->getHeader()['type']);
+        $this->assertEquals('event', $envelope->getItems()[1]->getHeader()['type']);
+
+        $this->assertEquals($payload, (string) $envelope);
+    }
+
+    private function getFixture(string $name): string
+    {
+        $fixture = file_get_contents(__DIR__ . "/fixtures/envelopes/{$name}.dat");
+
+        if ($fixture === false) {
+            throw new \RuntimeException("Failed to read fixture: {$name}");
+        }
+
+        // To make it easier to edit the fixtures, we remove the trailing new line
+        return rtrim($fixture, "\n");
+    }
+}
diff --git a/tests/fixtures/envelopes/envelope_with_2_items.dat b/tests/fixtures/envelopes/envelope_with_2_items.dat
new file mode 100644
index 0000000..8c0f57c
--- /dev/null
+++ b/tests/fixtures/envelopes/envelope_with_2_items.dat
@@ -0,0 +1,5 @@
+{"event_id":"9ec79c33ec9942ab8353589fcb2e04dc","dsn":"https:\/\/e12d836b15bb49d7bbf99e64295d995b:@sentry.io\/42"}
+{"type":"attachment","length":12,"content_type":"text\/plain","filename":"hello.txt"}
+Hello, world
+{"type":"event","length":41,"content_type":"application\/json","filename":"application.log"}
+{"message":"hello world","level":"error"}
diff --git a/tests/fixtures/envelopes/envelope_with_log_item.dat b/tests/fixtures/envelopes/envelope_with_log_item.dat
new file mode 100644
index 0000000..7c711df
--- /dev/null
+++ b/tests/fixtures/envelopes/envelope_with_log_item.dat
@@ -0,0 +1,3 @@
+{"event_id":"5b99b51b11c448668a2f7bb3d7cf326c","sent_at":"2025-05-07T19:58:25Z","dsn":"https:\/\/e12d836b15bb49d7bbf99e64295d995b:@sentry.io\/42","sdk":{"name":"sentry.php","version":"4.11.0"},"trace":{"trace_id":"e41ac4ffb6364fe2be41992a32118122","transaction":"<unlabeled transaction>","public_key":"37b2e15ddcf0af5695c1f12cb65afcdb","sampled":"false","sample_rand":"0.879018"}}
+{"type":"log","item_count":1,"content_type":"application\/vnd.sentry.items.log+json"}
+{"items":[{"timestamp":1746647905,"trace_id":"e41ac4ffb6364fe2be41992a32118122","level":"info","body":"Hello from the PHP SDK through the Agent!","attributes":{"sentry.environment":{"type":"string","value":"production"},"sentry.sdk.name":{"type":"string","value":"sentry.php"},"sentry.sdk.version":{"type":"string","value":"4.11.0"},"sentry.trace.parent_span_id":{"type":"string","value":"25dd80b92fa74189"}}}]}
diff --git a/tests/fixtures/envelopes/envelope_with_php_sdk_event.dat b/tests/fixtures/envelopes/envelope_with_php_sdk_event.dat
new file mode 100644
index 0000000..a413839
--- /dev/null
+++ b/tests/fixtures/envelopes/envelope_with_php_sdk_event.dat
@@ -0,0 +1,3 @@
+{"event_id":"b19688f4f3db401dbc7b49d954897516","sent_at":"2025-05-06T14:44:01Z","dsn":"https:\/\/e12d836b15bb49d7bbf99e64295d995b:@sentry.io\/42","sdk":{"name":"sentry.php","version":"4.10.0"},"trace":{"trace_id":"9b002d0fb3d0436cb40a3a643e080d76","public_key":"e12d836b15bb49d7bbf99e64295d995b"}}
+{"type":"event","content_type":"application\/json"}
+{"timestamp":1746542641.990966,"platform":"php","sdk":{"name":"sentry.php","version":"4.10.0"},"server_name":"Mac.localdomain","environment":"production","modules":{"clue\/mq-react":"v1.6.0","clue\/ndjson-react":"v1.3.0","composer\/pcre":"3.3.2","composer\/semver":"3.4.3","composer\/xdebug-handler":"3.0.5","evenement\/evenement":"v3.0.2","fidry\/cpu-core-counter":"1.2.0","fig\/http-message-util":"1.1.5","friendsofphp\/php-cs-fixer":"v3.72.0","guzzlehttp\/psr7":"2.7.0","jean85\/pretty-package-versions":"2.1.0","myclabs\/deep-copy":"1.13.1","nikic\/php-parser":"v5.4.0","phar-io\/manifest":"2.0.4","phar-io\/version":"3.2.1","phpstan\/phpstan":"2.1.8","phpunit\/php-code-coverage":"12.2.1","phpunit\/php-file-iterator":"6.0.0","phpunit\/php-invoker":"6.0.0","phpunit\/php-text-template":"5.0.0","phpunit\/php-timer":"8.0.0","phpunit\/phpunit":"12.1.4","psr\/container":"2.0.2","psr\/event-dispatcher":"1.0.0","psr\/http-factory":"1.1.0","psr\/http-message":"1.1","psr\/log":"3.0.2","ralouphie\/getallheaders":"3.0.3","react\/cache":"v1.2.0","react\/child-process":"v0.6.6","react\/dns":"v1.13.0","react\/event-loop":"v1.5.0","react\/http":"v1.11.0","react\/promise":"v3.2.0","react\/socket":"v1.16.0","react\/stream":"v1.4.0","sebastian\/cli-parser":"4.0.0","sebastian\/comparator":"7.0.1","sebastian\/complexity":"5.0.0","sebastian\/diff":"7.0.0","sebastian\/environment":"8.0.0","sebastian\/exporter":"7.0.0","sebastian\/global-state":"8.0.0","sebastian\/lines-of-code":"4.0.0","sebastian\/object-enumerator":"7.0.0","sebastian\/object-reflector":"5.0.0","sebastian\/recursion-context":"7.0.0","sebastian\/type":"6.0.2","sebastian\/version":"6.0.0","sentry\/sentry":"4.10.0","sentry\/sentry-agent":"dev-main@8a1ba3b","staabm\/side-effects-detector":"1.0.5","symfony\/console":"v7.2.1","symfony\/deprecation-contracts":"v3.5.1","symfony\/event-dispatcher":"v7.2.0","symfony\/event-dispatcher-contracts":"v3.5.1","symfony\/filesystem":"v7.2.0","symfony\/finder":"v7.2.2","symfony\/options-resolver":"v7.2.0","symfony\/polyfill-ctype":"v1.31.0","symfony\/polyfill-intl-grapheme":"v1.31.0","symfony\/polyfill-intl-normalizer":"v1.31.0","symfony\/polyfill-mbstring":"v1.31.0","symfony\/polyfill-php80":"v1.31.0","symfony\/polyfill-php81":"v1.31.0","symfony\/process":"v7.2.4","symfony\/service-contracts":"v3.5.1","symfony\/stopwatch":"v7.2.4","symfony\/string":"v7.2.0","theseer\/tokenizer":"1.2.3"},"contexts":{"os":{"name":"Darwin","version":"24.4.0","build":"Darwin Kernel Version 24.4.0: Fri Apr 11 18:33:40 PDT 2025; root:xnu-11417.101.15~117\/RELEASE_ARM64_T6031","kernel_version":"Darwin Mac.localdomain 24.4.0 Darwin Kernel Version 24.4.0: Fri Apr 11 18:33:40 PDT 2025; root:xnu-11417.101.15~117\/RELEASE_ARM64_T6031 arm64"},"runtime":{"name":"php","sapi":"cli","version":"8.4.5"},"trace":{"trace_id":"9b002d0fb3d0436cb40a3a643e080d76","span_id":"a8287de017514245"}},"message":"Hello world!"}