diff --git a/src/contact.ts b/src/contact.ts
index 4caef4d..905d35c 100644
--- a/src/contact.ts
+++ b/src/contact.ts
@@ -1,14 +1,16 @@
 import accounts from '../config/account.json' with { type: 'json' }
 import dkim from '../config/dkim.json' with { type: 'json' }
 
+export type AddressString = `${string}@${string}.${string}`
+
 export class Contact {
 	#name: string
-	#address: `${string}@${string}.${string}`
+	#address: AddressString
 
 	constructor(
 		{ name, address }: {
 			name: string
-			address: `${string}@${string}.${string}`
+			address: AddressString
 		},
 	) {
 		this.#name = name
@@ -60,18 +62,18 @@ export class Contact {
 		return `${this.#name} <${this.#address}>`
 	}
 
-	toJSON() {
+	toJSON(): { name: string; address: AddressString } {
 		return {
 			name: this.#name,
 			address: this.#address,
 		} as const
 	}
 
-	get name() {
+	get name(): string {
 		return this.#name
 	}
 
-	get address() {
+	get address(): AddressString {
 		return this.#address
 	}
 }