diff --git a/src/PhpImap/DataPartInfo.php b/src/PhpImap/DataPartInfo.php
index 38ece3e9..24d6541b 100644
--- a/src/PhpImap/DataPartInfo.php
+++ b/src/PhpImap/DataPartInfo.php
@@ -29,7 +29,7 @@ class DataPartInfo
     public $encoding;
 
     /** @var string|null */
-    public $charset;
+    public ?string $charset = null;
 
     /**
      * @var string|int
@@ -43,17 +43,17 @@ class DataPartInfo
      *
      * @readonly
      */
-    public $mail;
+    public Mailbox $mail;
 
     /**
      * @var int
      *
      * @readonly
      */
-    public $options;
+    public int $options;
 
     /** @var string|null */
-    protected $data;
+    protected ?string $data = null;
 
     /**
      * @param string|int $id
diff --git a/src/PhpImap/IncomingMail.php b/src/PhpImap/IncomingMail.php
index 8d532e5c..3ab3e5d1 100644
--- a/src/PhpImap/IncomingMail.php
+++ b/src/PhpImap/IncomingMail.php
@@ -21,23 +21,23 @@ class IncomingMail extends IncomingMailHeader
     /**
      * @var IncomingMailAttachment[]
      */
-    protected $attachments = [];
+    protected array $attachments = [];
 
     /** @var bool */
-    protected $hasAttachments = false;
+    protected bool $hasAttachments = false;
 
     /**
      * @var DataPartInfo[][]
      *
      * @psalm-var array{0:list<DataPartInfo>, 1:list<DataPartInfo>}
      */
-    protected $dataInfo = [[], []];
+    protected array $dataInfo = [[], []];
 
     /** @var string|null */
-    private $textPlain;
+    private ?string $textPlain = null;
 
     /** @var string|null */
-    private $textHtml;
+    private ?string $textHtml = null;
 
     public function setHeader(IncomingMailHeader $header): void
     {
diff --git a/src/PhpImap/IncomingMailAttachment.php b/src/PhpImap/IncomingMailAttachment.php
index e39bf9db..1c913922 100644
--- a/src/PhpImap/IncomingMailAttachment.php
+++ b/src/PhpImap/IncomingMailAttachment.php
@@ -17,36 +17,36 @@
 class IncomingMailAttachment
 {
     /** @var string|null */
-    public $id;
+    public ?string $id = null;
 
     /** @var string|null */
-    public $contentId;
+    public ?string $contentId = null;
 
     /** @var string|null */
-    public $name;
+    public ?string $name = null;
 
     /** @var string|null */
-    public $disposition;
+    public ?string $disposition = null;
 
     /** @var string|null */
-    public $charset;
+    public ?string $charset = null;
 
     /** @var bool|null */
-    public $emlOrigin;
+    public ?bool $emlOrigin = null;
 
     /** @var string|null */
-    private $file_path;
+    private ?string $file_path = null;
 
     /** @var DataPartInfo|null */
-    private $dataInfo;
+    private ?DataPartInfo $dataInfo = null;
 
     /**
      * @var string|null
      */
-    private $mimeType;
+    private ?string $mimeType = null;
 
     /** @var string|null */
-    private $filePath;
+    private ?string $filePath = null;
 
     public function __get(string $name)
     {
diff --git a/src/PhpImap/IncomingMailHeader.php b/src/PhpImap/IncomingMailHeader.php
index 0879f1fa..feb11413 100644
--- a/src/PhpImap/IncomingMailHeader.php
+++ b/src/PhpImap/IncomingMailHeader.php
@@ -12,90 +12,90 @@
 class IncomingMailHeader
 {
     /** @var string|null $id The IMAP message ID - not the "Message-ID:"-header of the email */
-    public $id;
+    public ?string $id = null;
 
     /** @var bool */
-    public $isDraft = false;
+    public bool $isDraft = false;
 
     /** @var string|null */
-    public $date;
+    public ?string $date = null;
 
     /** @var string|null */
-    public $headersRaw;
+    public ?string $headersRaw = null;
 
     /** @var object|null */
-    public $headers;
+    public ?object $headers = null;
 
     /** @var string|null */
-    public $priority;
+    public ?string $priority = null;
 
     /** @var string|null */
-    public $importance;
+    public ?string $importance = null;
 
     /** @var string|null */
-    public $sensitivity;
+    public ?string $sensitivity = null;
 
     /** @var string|null */
-    public $autoSubmitted;
+    public ?string $autoSubmitted = null;
 
     /** @var string|null */
-    public $precedence;
+    public ?string $precedence = null;
 
     /** @var string|null */
-    public $failedRecipients;
+    public ?string $failedRecipients = null;
 
     /** @var string|null */
-    public $subject;
+    public ?string $subject = null;
 
     /** @var string|null */
-    public $fromHost;
+    public ?string $fromHost = null;
 
     /** @var string|null */
-    public $fromName;
+    public ?string $fromName = null;
 
     /** @var string|null */
-    public $fromAddress;
+    public ?string $fromAddress = null;
 
     /** @var string|null */
-    public $senderHost;
+    public ?string $senderHost = null;
 
     /** @var string|null */
-    public $senderName;
+    public ?string $senderName = null;
 
     /** @var string|null */
-    public $senderAddress;
+    public ?string $senderAddress = null;
 
     /**
      * @var (string|null)[]
      *
      * @psalm-var array<string, string|null>
      */
-    public $to = [];
+    public array $to = [];
 
     /** @var string|null */
-    public $toString;
+    public ?string $toString = null;
 
     /**
      * @var (string|null)[]
      *
      * @psalm-var array<string, string|null>
      */
-    public $cc = [];
+    public array $cc = [];
 
     /**
      * @var (string|null)[]
      *
      * @psalm-var array<string, string|null>
      */
-    public $bcc = [];
+    public array $bcc = [];
 
     /**
      * @var (string|null)[]
      *
      * @psalm-var array<string, string|null>
      */
-    public $replyTo = [];
+    public array $replyTo = [];
 
     /** @var string|null */
-    public $messageId;
+    public ?string $messageId = null;
 }
diff --git a/src/PhpImap/Mailbox.php b/src/PhpImap/Mailbox.php
index 8d3f20ae..a0de8e1f 100644
--- a/src/PhpImap/Mailbox.php
+++ b/src/PhpImap/Mailbox.php
@@ -34,56 +34,56 @@
 class Mailbox
 {
     /** @var string */
-    protected $imapPath;
+    protected string $imapPath;
 
     /** @var string */
-    protected $imapLogin;
+    protected string $imapLogin;
 
     /** @var string */
-    protected $imapPassword;
+    protected string $imapPassword;
 
     /** @var string|null */
-    protected $imapOAuthAccessToken = null;
+    protected ?string $imapOAuthAccessToken = null;
 
     /** @var int */
-    protected $imapSearchOption = SE_UID;
+    protected int $imapSearchOption = SE_UID;
 
     /** @var int */
-    protected $connectionRetry = 0;
+    protected int $connectionRetry = 0;
 
     /** @var int */
-    protected $connectionRetryDelay = 100;
+    protected int $connectionRetryDelay = 100;
 
     /** @var int */
-    protected $imapOptions = 0;
+    protected int $imapOptions = 0;
 
     /** @var int */
-    protected $imapRetriesNum = 0;
+    protected int $imapRetriesNum = 0;
 
     /** @var array */
-    protected $imapParams = [];
+    protected array $imapParams = [];
 
     /** @var string */
-    protected $serverEncoding = 'UTF-8';
+    protected string $serverEncoding = 'UTF-8';
 
     /** @var string|null */
-    protected $attachmentsDir = null;
+    protected ?string $attachmentsDir = null;
 
     /** @var bool */
-    protected $expungeOnDisconnect = true;
+    protected bool $expungeOnDisconnect = true;
 
     /**
      * @var int[]
      *
      * @psalm-var array{1?:int, 2?:int, 3?:int, 4?:int}
      */
-    protected $timeouts = [];
+    protected array $timeouts = [];
 
     /** @var bool */
-    protected $attachmentsIgnore = false;
+    protected bool $attachmentsIgnore = false;
 
     /** @var string */
-    protected $pathDelimiter = '.';
+    protected string $pathDelimiter = '.';
 
     /** @var resource|null */
     private $imapStream;