diff --git a/packages/backend/migration/1703658526000-supportTrueMailApi.js b/packages/backend/migration/1703658526000-supportTrueMailApi.js
new file mode 100644
index 0000000000..0054d54122
--- /dev/null
+++ b/packages/backend/migration/1703658526000-supportTrueMailApi.js
@@ -0,0 +1,20 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and other misskey contributors
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+export class SupportTrueMailApi1703658526000 {
+    name = 'SupportTrueMailApi1703658526000'
+
+    async up(queryRunner) {
+    	  await queryRunner.query(`ALTER TABLE "meta" ADD "truemailInstance" character varying(1024)`);
+        await queryRunner.query(`ALTER TABLE "meta" ADD "truemailAuthKey" character varying(1024)`);
+        await queryRunner.query(`ALTER TABLE "meta" ADD "enableTruemailApi" boolean NOT NULL DEFAULT false`);
+    }
+
+    async down(queryRunner) {
+        await queryRunner.query(`ALTER TABLE "meta" DROP COLUMN "enableTruemailApi"`);
+        await queryRunner.query(`ALTER TABLE "meta" DROP COLUMN "truemailInstance"`);
+        await queryRunner.query(`ALTER TABLE "meta" DROP COLUMN "truemailAuthKey"`);
+    }
+}
diff --git a/packages/backend/src/core/EmailService.ts b/packages/backend/src/core/EmailService.ts
index 7fc7800783..7e812b4df2 100644
--- a/packages/backend/src/core/EmailService.ts
+++ b/packages/backend/src/core/EmailService.ts
@@ -156,7 +156,7 @@ export class EmailService {
 	@bindThis
 	public async validateEmailForAccount(emailAddress: string): Promise<{
 		available: boolean;
-		reason: null | 'used' | 'format' | 'disposable' | 'mx' | 'smtp' | 'banned';
+		reason: null | 'used' | 'format' | 'disposable' | 'mx' | 'smtp' | 'banned' | 'network' | 'blacklist';
 	}> {
 		const meta = await this.metaService.fetch();
 
@@ -173,6 +173,8 @@ export class EmailService {
 		if (meta.enableActiveEmailValidation) {
 			if (meta.enableVerifymailApi && meta.verifymailAuthKey != null) {
 				validated = await this.verifyMail(emailAddress, meta.verifymailAuthKey);
+			} else if (meta.enableTruemailApi && meta.truemailInstance && meta.truemailAuthKey != null) {
+				validated = await this.trueMail(meta.truemailInstance, emailAddress, meta.truemailAuthKey);
 			} else {
 				validated = await validateEmail({
 					email: emailAddress,
@@ -201,6 +203,8 @@ export class EmailService {
 			validated.reason === 'disposable' ? 'disposable' :
 			validated.reason === 'mx' ? 'mx' :
 			validated.reason === 'smtp' ? 'smtp' :
+			validated.reason === 'network' ? 'network' :
+			validated.reason === 'blacklist' ? 'blacklist' :
 			null,
 		};
 	}
@@ -265,4 +269,67 @@ export class EmailService {
 			reason: null,
 		};
 	}
+
+	private async trueMail<T>(truemailInstance: string, emailAddress: string, truemailAuthKey: string): Promise<{
+		valid: boolean;
+		reason: 'used' | 'format' | 'blacklist' | 'mx' | 'smtp' | 'network' | T | null;
+	}> {
+		const endpoint = truemailInstance + '?email=' + emailAddress;
+		try {
+			const res = await this.httpRequestService.send(endpoint, {
+				method: 'POST',
+				headers: {
+					'Content-Type': 'application/json',
+					Accept: 'application/json',
+					Authorization: truemailAuthKey
+				},
+			});
+			
+			const json = (await res.json()) as {
+				email: string;
+				success: boolean;
+				errors?: { 
+					list_match?: string;
+					regex?: string;
+					mx?: string;
+					smtp?: string;
+				} | null;
+			};
+			
+			if (json.email === undefined || (json.email !== undefined && json.errors?.regex)) {
+				return {
+						valid: false,
+						reason: 'format',
+				};
+			}
+			if (json.errors?.smtp) {
+				return {
+					valid: false,
+					reason: 'smtp',
+				};
+			}
+			if (json.errors?.mx) {
+				return {
+					valid: false,
+					reason: 'mx',
+				};
+			}
+			if (!json.success) {
+				return {
+					valid: false,
+					reason: json.errors?.list_match as T || 'blacklist',
+				};
+			}
+			
+			return {
+				valid: true,
+				reason: null,
+			};
+		} catch (error) {
+			return {
+				valid: false,
+				reason: 'network',
+			};
+		}
+	}
 }
diff --git a/packages/backend/src/models/Meta.ts b/packages/backend/src/models/Meta.ts
index 84ca762492..f5a75ed28a 100644
--- a/packages/backend/src/models/Meta.ts
+++ b/packages/backend/src/models/Meta.ts
@@ -457,6 +457,23 @@ export class MiMeta {
 	})
 	public verifymailAuthKey: string | null;
 
+	@Column('boolean', {
+		default: false,
+	})
+	public enableTruemailApi: boolean;
+
+	@Column('varchar', {
+		length: 1024,
+		nullable: true,
+	})
+	public truemailInstance: string | null;
+	
+	@Column('varchar', {
+		length: 1024,
+		nullable: true,
+	})
+	public truemailAuthKey: string | null;
+
 	@Column('boolean', {
 		default: true,
 	})
diff --git a/packages/backend/src/server/api/endpoints/admin/meta.ts b/packages/backend/src/server/api/endpoints/admin/meta.ts
index febc4ab1b1..281f6c484c 100644
--- a/packages/backend/src/server/api/endpoints/admin/meta.ts
+++ b/packages/backend/src/server/api/endpoints/admin/meta.ts
@@ -284,6 +284,18 @@ export const meta = {
 				type: 'string',
 				optional: false, nullable: true,
 			},
+			enableTruemailApi: {
+				type: 'boolean',
+				optional: false, nullable: false,
+			},
+			truemailInstance: {
+				type: 'string',
+				optional: false, nullable: true,
+			},
+			truemailAuthKey: {
+				type: 'string',
+				optional: false, nullable: true,
+			},
 			enableChartsForRemoteUser: {
 				type: 'boolean',
 				optional: false, nullable: false,
@@ -520,6 +532,9 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 				enableActiveEmailValidation: instance.enableActiveEmailValidation,
 				enableVerifymailApi: instance.enableVerifymailApi,
 				verifymailAuthKey: instance.verifymailAuthKey,
+				enableTruemailApi: instance.enableTruemailApi,
+				truemailInstance: instance.truemailInstance,
+				truemailAuthKey: instance.truemailAuthKey,
 				enableChartsForRemoteUser: instance.enableChartsForRemoteUser,
 				enableChartsForFederatedInstances: instance.enableChartsForFederatedInstances,
 				enableServerMachineStats: instance.enableServerMachineStats,
diff --git a/packages/backend/src/server/api/endpoints/admin/update-meta.ts b/packages/backend/src/server/api/endpoints/admin/update-meta.ts
index 5a215696fb..3a6426435d 100644
--- a/packages/backend/src/server/api/endpoints/admin/update-meta.ts
+++ b/packages/backend/src/server/api/endpoints/admin/update-meta.ts
@@ -116,6 +116,9 @@ export const paramDef = {
 		enableActiveEmailValidation: { type: 'boolean' },
 		enableVerifymailApi: { type: 'boolean' },
 		verifymailAuthKey: { type: 'string', nullable: true },
+		enableTruemailApi: { type: 'boolean' },
+		truemailInstance: { type: 'string', nullable: true },
+		truemailAuthKey: { type: 'string', nullable: true },
 		enableChartsForRemoteUser: { type: 'boolean' },
 		enableChartsForFederatedInstances: { type: 'boolean' },
 		enableServerMachineStats: { type: 'boolean' },
@@ -469,6 +472,26 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 					set.verifymailAuthKey = ps.verifymailAuthKey;
 				}
 			}
+			
+			if (ps.enableTruemailApi !== undefined) {
+				set.enableTruemailApi = ps.enableTruemailApi;
+			}
+
+			if (ps.truemailInstance !== undefined) {
+				if (ps.truemailInstance === '') {
+					set.truemailInstance = null;
+				} else {
+					set.truemailInstance = ps.truemailInstance;
+				}
+			}
+
+			if (ps.truemailAuthKey !== undefined) {
+				if (ps.truemailAuthKey === '') {
+					set.truemailAuthKey = null;
+				} else {
+					set.truemailAuthKey = ps.truemailAuthKey;
+				}
+			}
 
 			if (ps.enableChartsForRemoteUser !== undefined) {
 				set.enableChartsForRemoteUser = ps.enableChartsForRemoteUser;
diff --git a/packages/frontend/src/pages/admin/security.vue b/packages/frontend/src/pages/admin/security.vue
index 7070157ca9..8d79dea20f 100644
--- a/packages/frontend/src/pages/admin/security.vue
+++ b/packages/frontend/src/pages/admin/security.vue
@@ -80,6 +80,17 @@ SPDX-License-Identifier: AGPL-3.0-only
 							<template #prefix><i class="ti ti-key"></i></template>
 							<template #label>Verifymail.io API Auth Key</template>
 						</MkInput>
+						<MkSwitch v-model="enableTruemailApi" @update:modelValue="save">
+							<template #label>Use TrueMail API</template>
+						</MkSwitch>
+						<MkInput v-model="truemailInstance" @update:modelValue="save">
+							<template #prefix><i class="ti ti-key"></i></template>
+							<template #label>TrueMail API Instance</template>
+						</MkInput>
+						<MkInput v-model="truemailAuthKey" @update:modelValue="save">
+							<template #prefix><i class="ti ti-key"></i></template>
+							<template #label>TrueMail API Auth Key</template>
+						</MkInput>
 					</div>
 				</MkFolder>
 
@@ -153,6 +164,9 @@ const enableIpLogging = ref<boolean>(false);
 const enableActiveEmailValidation = ref<boolean>(false);
 const enableVerifymailApi = ref<boolean>(false);
 const verifymailAuthKey = ref<string | null>(null);
+const enableTruemailApi = ref<boolean>(false);
+const truemailInstance = ref<string | null>(null);
+const truemailAuthKey = ref<string | null>(null);
 const bannedEmailDomains = ref<string>('');
 
 async function init() {
@@ -194,6 +208,9 @@ function save() {
 		enableActiveEmailValidation: enableActiveEmailValidation.value,
 		enableVerifymailApi: enableVerifymailApi.value,
 		verifymailAuthKey: verifymailAuthKey.value,
+		enableTruemailApi: enableTruemailApi.value,
+		truemailInstance: truemailInstance.value,
+		truemailAuthKey: truemailAuthKey.value,
 		bannedEmailDomains: bannedEmailDomains.value.split('\n'),
 	}).then(() => {
 		fetchInstance();