diff --git a/CHANGELOG.md b/CHANGELOG.md
index 001ee38f..dcd4be75 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,13 @@ The file format of it is based on [Keep a Changelog](http://keepachangelog.com/e
 For public Changelog covering all changes done to Pipedrive’s API, webhooks and app extensions platforms, see [public Changelog](https://pipedrive.readme.io/docs/changelog) with discussion area in [Developers Community](https://devcommunity.pipedrive.com/c/documentation/changelog/19).
 
 ## [Unreleased]
+### Fixed
+- Marked fields that can be `null` as `nullable: true` in Mailbox endpoints:
+  - `draft`, `from[].linked_person_id`, `from[].linked_person_name` (and the same for `to`, `cc`, `bcc`) in `GET /v1/mailbox/mailMessages/{id}`
+  - `template_id`, plus the same `draft` and participant `linked_person_id` / `linked_person_name` fields, in `GET /v1/deals/{id}/mailMessages`, `GET /v1/persons/{id}/mailMessages` and `GET /v1/organizations/{id}/mailMessages`
+  - `snippet_sent`, `last_message_received_timestamp`, `archived_flag`, `drafts_parties`, `parties.to[].linked_person_id` and `parties.to[].linked_person_name` (and the same for `parties.from`) in `GET /v1/mailbox/mailThreads`, `GET /v1/mailbox/mailThreads/{id}` and `PUT /v1/mailbox/mailThreads/{id}`
+  - `from[].linked_person_id` and `from[].linked_person_name` (and the same for `to`, `cc`, `bcc`) in `GET /v1/mailbox/mailThreads/{id}/mailMessages`
+  - `deal_id` and `lead_id` in the `PUT /v1/mailbox/mailThreads/{id}` request body, where `null` unlinks the deal or lead
 
 ## [36.1.0] - 2026-10-21
 ### Added
diff --git a/src/versions/v1/models/mail-message-data-from-inner.ts b/src/versions/v1/models/mail-message-data-from-inner.ts
index d5057e4c..d2e61d14 100644
--- a/src/versions/v1/models/mail-message-data-from-inner.ts
+++ b/src/versions/v1/models/mail-message-data-from-inner.ts
@@ -39,12 +39,12 @@ export interface MailMessageDataFromInner {
     * ID of the linked person to the mail message
     * @type {number}
     */
-    'linked_person_id'?: number;
+    'linked_person_id'?: number | null;
     /**
     * Name of the linked person to the mail message
     * @type {string}
     */
-    'linked_person_name'?: string;
+    'linked_person_name'?: string | null;
     /**
     * ID of the mail message participant
     * @type {number}
diff --git a/src/versions/v1/models/mail-message-data.ts b/src/versions/v1/models/mail-message-data.ts
index d46681a5..0236fb22 100644
--- a/src/versions/v1/models/mail-message-data.ts
+++ b/src/versions/v1/models/mail-message-data.ts
@@ -102,7 +102,7 @@ export interface MailMessageData {
     * If the mail message has a draft status then the value is the mail message object as JSON formatted string, otherwise `null`.
     * @type {string}
     */
-    'draft'?: string;
+    'draft'?: string | null;
     /**
     * 
     * @type {number}
diff --git a/src/versions/v1/models/mail-message-item-for-list-all-of.ts b/src/versions/v1/models/mail-message-item-for-list-all-of.ts
index 3495bb31..22d5d69b 100644
--- a/src/versions/v1/models/mail-message-item-for-list-all-of.ts
+++ b/src/versions/v1/models/mail-message-item-for-list-all-of.ts
@@ -49,7 +49,7 @@ export interface MailMessageItemForListAllOf {
     * The ID of the mail template
     * @type {number}
     */
-    'template_id'?: number;
+    'template_id'?: number | null;
     /**
     * The add date and time of the Mail Message
     * @type {string}
diff --git a/src/versions/v1/models/mail-thread-all-of1-parties-to-inner.ts b/src/versions/v1/models/mail-thread-all-of1-parties-to-inner.ts
index a311e712..0adc80fa 100644
--- a/src/versions/v1/models/mail-thread-all-of1-parties-to-inner.ts
+++ b/src/versions/v1/models/mail-thread-all-of1-parties-to-inner.ts
@@ -49,12 +49,12 @@ export interface MailThreadAllOf1PartiesToInner {
     * ID of the linked person
     * @type {number}
     */
-    'linked_person_id'?: number;
+    'linked_person_id'?: number | null;
     /**
-    * Email of the linked person
+    * Name of the linked person
     * @type {string}
     */
-    'linked_person_name'?: string;
+    'linked_person_name'?: string | null;
     /**
     * ID of the mail message party
     * @type {number}
diff --git a/src/versions/v1/models/mail-thread-all-of1.ts b/src/versions/v1/models/mail-thread-all-of1.ts
index 1c60e0df..ba7573ec 100644
--- a/src/versions/v1/models/mail-thread-all-of1.ts
+++ b/src/versions/v1/models/mail-thread-all-of1.ts
@@ -29,10 +29,10 @@ export interface MailThreadAllOf1 {
     */
     'parties'?: MailThreadAllOf1Parties;
     /**
-    * Parties of the drafted mail thread
+    * Parties of the drafted mail thread. `null` if the mail thread has no drafts.
     * @type {Array<object>}
     */
-    'drafts_parties'?: Array<object>;
+    'drafts_parties'?: Array<object> | null;
     /**
     * Folders in which messages from thread are being stored
     * @type {Array<string>}
@@ -52,7 +52,7 @@ export interface MailThreadAllOf1 {
     * A snippet from a message sent
     * @type {string}
     */
-    'snippet_sent'?: string;
+    'snippet_sent'?: string | null;
     /**
     * An amount of messages
     * @type {number}
@@ -69,10 +69,10 @@ export interface MailThreadAllOf1 {
     */
     'has_sent_flag'?: MailThreadAllOf1HasSentFlagConst;
     /**
-    * 
+    * Whether the mail thread is archived. `null` if the mail thread has not been explicitly archived or unarchived in Pipedrive.
     * @type {number}
     */
-    'archived_flag'?: MailThreadAllOf1ArchivedFlagConst;
+    'archived_flag'?: MailThreadAllOf1ArchivedFlagConst | null;
     /**
     * 
     * @type {number}
@@ -107,7 +107,7 @@ export interface MailThreadAllOf1 {
     * The last time when the mail thread has had a message received
     * @type {string}
     */
-    'last_message_received_timestamp'?: string;
+    'last_message_received_timestamp'?: string | null;
     /**
     * The time when the mail thread was inserted to database
     * @type {string}