diff --git a/tasks/release/HttpClient.php b/tasks/release/HttpClient.php
deleted file mode 100644
index 7240b23297..0000000000
--- a/tasks/release/HttpClient.php
+++ /dev/null
@@ -1,45 +0,0 @@
-<?php
-
-namespace MailPoetTasks\Release;
-
-class HttpClient {
-  /** @var string|null */
-  private $base_uri;
-
-  public function __construct($base_uri = null) {
-    $this->base_uri = $base_uri === null ? null : rtrim($base_uri, '/');
-  }
-
-  public function get($url) {
-    return $this->request($url, 'GET');
-  }
-
-  public function post($url, array $data) {
-    return $this->request($url, 'POST', $data);
-  }
-
-  public function put($url, array $data) {
-    return $this->request($url, 'PUT', $data);
-  }
-
-  private function request($path, $method, array $data = null) {
-    $url = $this->base_uri === null ? $path : ("$this->base_uri/" . ltrim($path, '/'));
-    $options = [];
-    if ($method === 'POST' || $method === 'PUT') {
-      $options = [
-        'http' => [
-          'method' => $method,
-          'header' => "Content-type: application/json\r\n",
-          'content' => json_encode($data, JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES),
-        ]
-      ];
-    }
-    $context = stream_context_create($options);
-    $result = file_get_contents($url, false, $context);
-    if ($result === false) {
-      $error = error_get_last();
-      throw new \Exception('Request error: ' . $error['message']);
-    }
-    return json_decode($result, true);
-  }
-}
diff --git a/tasks/release/JiraController.php b/tasks/release/JiraController.php
index 57c519541a..633f68ecc4 100644
--- a/tasks/release/JiraController.php
+++ b/tasks/release/JiraController.php
@@ -2,6 +2,8 @@
 
 namespace MailPoetTasks\Release;
 
+use GuzzleHttp\Client;
+
 class JiraController {
 
   const CHANGELOG_FIELD_ID = 'customfield_10500';
@@ -24,7 +26,7 @@ class JiraController {
   /** @var string */
   private $project;
 
-  /** @var HttpClient */
+  /** @var Client */
   private $http_client;
 
   public function __construct($token, $user, $project) {
@@ -37,14 +39,15 @@ class JiraController {
     $jira_domain = self::JIRA_DOMAIN;
     $jira_api_version = self::JIRA_API_VERSION;
     $base_uri = "https://$url_user:$url_token@$jira_domain/rest/api/$jira_api_version/";
-    $this->http_client = new HttpClient($base_uri);
+    $this->http_client = new Client(['base_uri' => $base_uri]);
   }
 
   /**
    * @see https://developer.atlassian.com/cloud/jira/platform/rest/v3/#api-api-3-project-projectIdOrKey-versions-get
    */
   function getVersion($version_name = null) {
-    $versions = $this->http_client->get("project/$this->project/versions");
+    $response = $this->http_client->get("project/$this->project/versions");
+    $versions = json_decode($response->getBody()->getContents(), true);
     if ($version_name === null) {
       return end($versions);
     }
@@ -66,7 +69,8 @@ class JiraController {
       'released' => false,
       'project' => $this->project,
     ];
-    return $this->http_client->post('/version', $data);
+    $response = $this->http_client->post('version', ['json' => $data]);
+    return json_decode($response->getBody()->getContents(), true);
   }
 
   function getIssuesDataForVersion($version) {
@@ -93,13 +97,14 @@ class JiraController {
     if ($fields) {
       $params['fields'] = join(',', $fields);
     }
-    return $this->http_client->get('/search?' . http_build_query($params));
+    $response = $this->http_client->get('search', ['query' => $params]);
+    return json_decode($response->getBody()->getContents(), true);
   }
 
   /**
    * @see https://developer.atlassian.com/cloud/jira/platform/rest/v3/#api-api-3-issue-issueIdOrKey-put
    */
   function updateIssue($key, $data) {
-    $this->http_client->put("/issue/$key", $data);
+    $this->http_client->put("issue/$key", ['json' => $data]);
   }
 }
diff --git a/tasks/release/SlackNotifier.php b/tasks/release/SlackNotifier.php
index 03b3983a10..297acb0e1a 100644
--- a/tasks/release/SlackNotifier.php
+++ b/tasks/release/SlackNotifier.php
@@ -2,6 +2,8 @@
 
 namespace MailPoetTasks\Release;
 
+use GuzzleHttp\Client;
+
 class SlackNotifier {
   const PROJECT_MAILPOET = 'MAILPOET';
   const PROJECT_PREMIUM = 'PREMIUM';
@@ -12,13 +14,13 @@ class SlackNotifier {
   /** @var string */
   private $project;
 
-  /** @var HttpClient */
+  /** @var Client */
   private $http_client;
 
   public function __construct($webhook_url, $project) {
     $this->webhook_url = $webhook_url;
     $this->project = $project;
-    $this->http_client = new HttpClient();
+    $this->http_client = new Client();
   }
 
   public function notify($version, $changelog, $release_id) {
@@ -50,8 +52,10 @@ class SlackNotifier {
     $message = preg_replace(['/&/u', '/</u', '/>/u'], ['&amp;', '&lt;', '&gt;'], $message);
 
     $this->http_client->post($this->webhook_url, [
-      'text' => $message,
-      'unfurl_links' => false,
+      'json' => [
+        'text' => $message,
+        'unfurl_links' => false,
+      ],
     ]);
   }
 }