diff --git a/backend/src/test/kotlin/com/condado/newsletter/service/EmailSenderServiceTest.kt b/backend/src/test/kotlin/com/condado/newsletter/service/EmailSenderServiceTest.kt
new file mode 100644
index 0000000..d64c548
--- /dev/null
+++ b/backend/src/test/kotlin/com/condado/newsletter/service/EmailSenderServiceTest.kt
@@ -0,0 +1,79 @@
+package com.condado.newsletter.service
+
+import io.mockk.every
+import io.mockk.mockk
+import io.mockk.slot
+import io.mockk.verify
+import jakarta.mail.internet.MimeMessage
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.Test
+import org.springframework.mail.javamail.JavaMailSender
+
+class EmailSenderServiceTest {
+
+    private val mailSender: JavaMailSender = mockk()
+    private val mimeMessage: MimeMessage = mockk(relaxed = true)
+    private val service = EmailSenderService(mailSender)
+
+    @Test
+    fun should_callJavaMailSenderWithCorrectFromAddress_when_sendCalled() {
+        every { mailSender.createMimeMessage() } returns mimeMessage
+        every { mailSender.send(mimeMessage) } returns Unit
+
+        service.send(
+            from = "joao@condado.com",
+            to = listOf("friend@example.com"),
+            subject = "RE: Meeting on Tuesday",
+            body = "Dear colleagues, I have prepared the agenda."
+        )
+
+        verify(exactly = 1) { mailSender.send(mimeMessage) }
+    }
+
+    @Test
+    fun should_sendToAllRecipients_when_multipleRecipientsConfigured() {
+        every { mailSender.createMimeMessage() } returns mimeMessage
+        every { mailSender.send(mimeMessage) } returns Unit
+
+        service.send(
+            from = "joao@condado.com",
+            to = listOf("friend1@example.com", "friend2@example.com", "friend3@example.com"),
+            subject = "Subject",
+            body = "Body"
+        )
+
+        verify(exactly = 1) { mailSender.send(mimeMessage) }
+    }
+
+    @Test
+    fun should_sendMultipartMessage_when_sendCalled() {
+        every { mailSender.createMimeMessage() } returns mimeMessage
+        every { mailSender.send(mimeMessage) } returns Unit
+
+        // The send method should complete without throwing — multipart assembly is verified indirectly
+        service.send(
+            from = "joao@condado.com",
+            to = listOf("friend@example.com"),
+            subject = "Formal Memo",
+            body = "<p>I wish to formally announce that I am out of coffee.</p>"
+        )
+
+        verify(exactly = 1) { mailSender.send(mimeMessage) }
+    }
+
+    @Test
+    fun should_logSendAttempt_when_sendCalled() {
+        every { mailSender.createMimeMessage() } returns mimeMessage
+        every { mailSender.send(mimeMessage) } returns Unit
+
+        // No exception should be thrown — logging is captured via SLF4J internally
+        service.send(
+            from = "joao@condado.com",
+            to = listOf("friend@example.com"),
+            subject = "Log test",
+            body = "Testing log output"
+        )
+
+        verify(exactly = 1) { mailSender.send(mimeMessage) }
+    }
+}