diff --git a/app/core/src/main/java/com/fsck/k9/backend/ImapBackendFactory.kt b/app/core/src/main/java/com/fsck/k9/backend/ImapBackendFactory.kt
index 79b4a2409..226ed2269 100644
--- a/app/core/src/main/java/com/fsck/k9/backend/ImapBackendFactory.kt
+++ b/app/core/src/main/java/com/fsck/k9/backend/ImapBackendFactory.kt
@@ -10,6 +10,7 @@ import com.fsck.k9.mail.oauth.OAuth2TokenProvider
 import com.fsck.k9.mail.power.PowerManager
 import com.fsck.k9.mail.ssl.DefaultTrustedSocketFactory
 import com.fsck.k9.mail.store.imap.ImapStore
+import com.fsck.k9.mail.transport.smtp.SmtpTransport
 import com.fsck.k9.mailstore.K9BackendStorage
 
 class ImapBackendFactory(
@@ -22,7 +23,8 @@ class ImapBackendFactory(
         val accountName = account.description
         val backendStorage = K9BackendStorage(preferences, account, account.localStore)
         val imapStore = createImapStore(account)
-        return ImapBackend(accountName, backendStorage, imapStore, powerManager)
+        val smtpTransport = createSmtpTransport(account)
+        return ImapBackend(accountName, backendStorage, imapStore, powerManager, smtpTransport)
     }
 
     private fun createImapStore(account: Account): ImapStore {
@@ -34,4 +36,9 @@ class ImapBackendFactory(
                 oAuth2TokenProvider
         )
     }
+
+    private fun createSmtpTransport(account: Account): SmtpTransport {
+        val oauth2TokenProvider: OAuth2TokenProvider? = null
+        return SmtpTransport(account, DefaultTrustedSocketFactory(context), oauth2TokenProvider)
+    }
 }
diff --git a/app/core/src/main/java/com/fsck/k9/backend/Pop3BackendFactory.kt b/app/core/src/main/java/com/fsck/k9/backend/Pop3BackendFactory.kt
index b5e65f953..5b6088563 100644
--- a/app/core/src/main/java/com/fsck/k9/backend/Pop3BackendFactory.kt
+++ b/app/core/src/main/java/com/fsck/k9/backend/Pop3BackendFactory.kt
@@ -5,8 +5,10 @@ import com.fsck.k9.Account
 import com.fsck.k9.Preferences
 import com.fsck.k9.backend.api.Backend
 import com.fsck.k9.backend.pop3.Pop3Backend
+import com.fsck.k9.mail.oauth.OAuth2TokenProvider
 import com.fsck.k9.mail.ssl.DefaultTrustedSocketFactory
 import com.fsck.k9.mail.store.pop3.Pop3Store
+import com.fsck.k9.mail.transport.smtp.SmtpTransport
 import com.fsck.k9.mailstore.K9BackendStorage
 
 class Pop3BackendFactory(private val context: Context, private val preferences: Preferences) : BackendFactory {
@@ -15,10 +17,16 @@ class Pop3BackendFactory(private val context: Context, private val preferences:
         val accountName = account.description
         val backendStorage = K9BackendStorage(preferences, account, account.localStore)
         val pop3Store = createPop3Store(account)
-        return Pop3Backend(accountName, backendStorage, pop3Store)
+        val smtpTransport = createSmtpTransport(account)
+        return Pop3Backend(accountName, backendStorage, pop3Store, smtpTransport)
     }
 
     private fun createPop3Store(account: Account): Pop3Store {
         return Pop3Store(account, DefaultTrustedSocketFactory(context))
     }
+
+    private fun createSmtpTransport(account: Account): SmtpTransport {
+        val oauth2TokenProvider: OAuth2TokenProvider? = null
+        return SmtpTransport(account, DefaultTrustedSocketFactory(context), oauth2TokenProvider)
+    }
 }
diff --git a/app/core/src/main/java/com/fsck/k9/backend/WebDavBackendFactory.kt b/app/core/src/main/java/com/fsck/k9/backend/WebDavBackendFactory.kt
index f8466c665..5fdddc6fd 100644
--- a/app/core/src/main/java/com/fsck/k9/backend/WebDavBackendFactory.kt
+++ b/app/core/src/main/java/com/fsck/k9/backend/WebDavBackendFactory.kt
@@ -5,6 +5,7 @@ import com.fsck.k9.Preferences
 import com.fsck.k9.backend.api.Backend
 import com.fsck.k9.backend.webdav.WebDavBackend
 import com.fsck.k9.mail.store.webdav.WebDavStore
+import com.fsck.k9.mail.transport.WebDavTransport
 import com.fsck.k9.mailstore.K9BackendStorage
 
 class WebDavBackendFactory(private val preferences: Preferences) : BackendFactory {
@@ -13,7 +14,8 @@ class WebDavBackendFactory(private val preferences: Preferences) : BackendFactor
         val accountName = account.description
         val backendStorage = K9BackendStorage(preferences, account, account.localStore)
         val webDavStore = createWebDavStore(account)
-        return WebDavBackend(accountName, backendStorage, webDavStore)
+        val webDavTransport = WebDavTransport(account)
+        return WebDavBackend(accountName, backendStorage, webDavStore, webDavTransport)
     }
 
     private fun createWebDavStore(account: Account): WebDavStore {
diff --git a/app/core/src/main/java/com/fsck/k9/controller/MessagingController.java b/app/core/src/main/java/com/fsck/k9/controller/MessagingController.java
index 130eb544f..8784713d8 100644
--- a/app/core/src/main/java/com/fsck/k9/controller/MessagingController.java
+++ b/app/core/src/main/java/com/fsck/k9/controller/MessagingController.java
@@ -71,8 +71,6 @@ import com.fsck.k9.mail.MessagingException;
 import com.fsck.k9.mail.Part;
 import com.fsck.k9.mail.PushReceiver;
 import com.fsck.k9.mail.Pusher;
-import com.fsck.k9.mail.Transport;
-import com.fsck.k9.mail.TransportProvider;
 import com.fsck.k9.mail.internet.MessageExtractor;
 import com.fsck.k9.mail.internet.MimeUtility;
 import com.fsck.k9.mailstore.LocalFolder;
@@ -128,7 +126,6 @@ public class MessagingController {
     private final ConcurrentHashMap<Account, Pusher> pushers = new ConcurrentHashMap<>();
     private final ExecutorService threadPool = Executors.newCachedThreadPool();
     private final MemorizingMessagingListener memorizingMessagingListener = new MemorizingMessagingListener();
-    private final TransportProvider transportProvider;
     private final AccountStatsCollector accountStatsCollector;
     private final CoreResourceProvider resourceProvider;
 
@@ -142,10 +139,9 @@ public class MessagingController {
             Context appContext = context.getApplicationContext();
             NotificationController notificationController = DI.get(NotificationController.class);
             Contacts contacts = Contacts.getInstance(context);
-            TransportProvider transportProvider = TransportProvider.getInstance();
             AccountStatsCollector accountStatsCollector = new DefaultAccountStatsCollector(context);
             CoreResourceProvider resourceProvider = DI.get(CoreResourceProvider.class);
-            inst = new MessagingController(appContext, notificationController, contacts, transportProvider,
+            inst = new MessagingController(appContext, notificationController, contacts,
                     accountStatsCollector, resourceProvider);
         }
         return inst;
@@ -154,12 +150,10 @@ public class MessagingController {
 
     @VisibleForTesting
     MessagingController(Context context, NotificationController notificationController, Contacts contacts,
-            TransportProvider transportProvider, AccountStatsCollector accountStatsCollector,
-            CoreResourceProvider resourceProvider) {
+            AccountStatsCollector accountStatsCollector, CoreResourceProvider resourceProvider) {
         this.context = context;
         this.notificationController = notificationController;
         this.contacts = contacts;
-        this.transportProvider = transportProvider;
         this.accountStatsCollector = accountStatsCollector;
         this.resourceProvider = resourceProvider;
 
@@ -1603,7 +1597,7 @@ public class MessagingController {
             Timber.i("Scanning folder '%s' (%d) for messages to send",
                     account.getOutboxFolder(), localFolder.getDatabaseId());
 
-            Transport transport = transportProvider.getTransport(context, account);
+            Backend backend = getBackend(account);
 
             for (LocalMessage message : localMessages) {
                 if (message.isSet(Flag.DELETED)) {
@@ -1638,7 +1632,7 @@ public class MessagingController {
                         message.setFlag(Flag.X_SEND_IN_PROGRESS, true);
 
                         Timber.i("Sending message with UID %s", message.getUid());
-                        transport.sendMessage(message);
+                        backend.sendMessage(message);
 
                         message.setFlag(Flag.X_SEND_IN_PROGRESS, false);
                         message.setFlag(Flag.SEEN, true);
diff --git a/app/core/src/test/java/com/fsck/k9/controller/MessagingControllerTest.java b/app/core/src/test/java/com/fsck/k9/controller/MessagingControllerTest.java
index 846686a25..53fc5676e 100644
--- a/app/core/src/test/java/com/fsck/k9/controller/MessagingControllerTest.java
+++ b/app/core/src/test/java/com/fsck/k9/controller/MessagingControllerTest.java
@@ -26,8 +26,6 @@ import com.fsck.k9.mail.Flag;
 import com.fsck.k9.mail.Folder;
 import com.fsck.k9.mail.MessageRetrievalListener;
 import com.fsck.k9.mail.MessagingException;
-import com.fsck.k9.mail.Transport;
-import com.fsck.k9.mail.TransportProvider;
 import com.fsck.k9.mailstore.LocalFolder;
 import com.fsck.k9.mailstore.LocalMessage;
 import com.fsck.k9.mailstore.LocalStore;
@@ -97,10 +95,6 @@ public class MessagingControllerTest extends K9RobolectricTest {
     private LocalStore localStore;
     @Mock
     private NotificationController notificationController;
-    @Mock
-    private TransportProvider transportProvider;
-    @Mock
-    private Transport transport;
     @Captor
     private ArgumentCaptor<List<LocalFolder>> localFolderListCaptor;
     @Captor
@@ -144,7 +138,7 @@ public class MessagingControllerTest extends K9RobolectricTest {
 
         MessagingControllerTestExtra.backendManagerProvides(backend);
 
-        controller = new MessagingController(appContext, notificationController, contacts, transportProvider,
+        controller = new MessagingController(appContext, notificationController, contacts,
                 accountStatsCollector, mock(CoreResourceProvider.class));
 
         configureAccount();
@@ -537,7 +531,7 @@ public class MessagingControllerTest extends K9RobolectricTest {
 
         controller.sendPendingMessagesSynchronous(account);
 
-        verify(transport).sendMessage(localMessageToSend1);
+        verify(backend).sendMessage(localMessageToSend1);
     }
 
     @Test
@@ -546,9 +540,9 @@ public class MessagingControllerTest extends K9RobolectricTest {
 
         controller.sendPendingMessagesSynchronous(account);
 
-        InOrder ordering = inOrder(localMessageToSend1, transport);
+        InOrder ordering = inOrder(localMessageToSend1, backend);
         ordering.verify(localMessageToSend1).setFlag(Flag.X_SEND_IN_PROGRESS, true);
-        ordering.verify(transport).sendMessage(localMessageToSend1);
+        ordering.verify(backend).sendMessage(localMessageToSend1);
         ordering.verify(localMessageToSend1).setFlag(Flag.X_SEND_IN_PROGRESS, false);
     }
 
@@ -582,7 +576,7 @@ public class MessagingControllerTest extends K9RobolectricTest {
     @Test
     public void sendPendingMessagesSynchronous_withAuthenticationFailure_shouldNotify() throws MessagingException {
         setupAccountWithMessageToSend();
-        doThrow(new AuthenticationFailedException("Test")).when(transport).sendMessage(localMessageToSend1);
+        doThrow(new AuthenticationFailedException("Test")).when(backend).sendMessage(localMessageToSend1);
 
         controller.sendPendingMessagesSynchronous(account);
 
@@ -592,7 +586,7 @@ public class MessagingControllerTest extends K9RobolectricTest {
     @Test
     public void sendPendingMessagesSynchronous_withCertificateFailure_shouldNotify() throws MessagingException {
         setupAccountWithMessageToSend();
-        doThrow(new CertificateValidationException("Test")).when(transport).sendMessage(localMessageToSend1);
+        doThrow(new CertificateValidationException("Test")).when(backend).sendMessage(localMessageToSend1);
 
         controller.sendPendingMessagesSynchronous(account);
 
@@ -615,7 +609,6 @@ public class MessagingControllerTest extends K9RobolectricTest {
         when(localStore.getFolder(SENT_FOLDER_NAME)).thenReturn(sentFolder);
         when(sentFolder.getDatabaseId()).thenReturn(1L);
         when(localFolder.exists()).thenReturn(true);
-        when(transportProvider.getTransport(appContext, account)).thenReturn(transport);
         when(localFolder.getMessages(null)).thenReturn(Collections.singletonList(localMessageToSend1));
         when(localMessageToSend1.getUid()).thenReturn("localMessageToSend1");
         when(localMessageToSend1.getHeader(K9.IDENTITY_HEADER)).thenReturn(new String[]{});
diff --git a/backend/api/src/main/java/com/fsck/k9/backend/api/Backend.kt b/backend/api/src/main/java/com/fsck/k9/backend/api/Backend.kt
index ab92f3350..3a0dd7490 100644
--- a/backend/api/src/main/java/com/fsck/k9/backend/api/Backend.kt
+++ b/backend/api/src/main/java/com/fsck/k9/backend/api/Backend.kt
@@ -83,4 +83,7 @@ interface Backend {
 
     @Throws(MessagingException::class)
     fun checkServerSettings()
+
+    @Throws(MessagingException::class)
+    fun sendMessage(message: Message)
 }
diff --git a/backend/imap/build.gradle b/backend/imap/build.gradle
index 107cd73af..1360526dd 100644
--- a/backend/imap/build.gradle
+++ b/backend/imap/build.gradle
@@ -13,6 +13,7 @@ dependencies {
 
     api project(":backend:api")
     implementation project(":mail:protocols:imap")
+    implementation project(":mail:protocols:smtp")
 
     implementation "com.jakewharton.timber:timber:${versions.timber}"
 
diff --git a/backend/imap/src/main/java/com/fsck/k9/backend/imap/ImapBackend.java b/backend/imap/src/main/java/com/fsck/k9/backend/imap/ImapBackend.java
index 021edf9e3..a391e47cc 100644
--- a/backend/imap/src/main/java/com/fsck/k9/backend/imap/ImapBackend.java
+++ b/backend/imap/src/main/java/com/fsck/k9/backend/imap/ImapBackend.java
@@ -22,6 +22,7 @@ import com.fsck.k9.mail.Pusher;
 import com.fsck.k9.mail.power.PowerManager;
 import com.fsck.k9.mail.store.imap.ImapPusher;
 import com.fsck.k9.mail.store.imap.ImapStore;
+import com.fsck.k9.mail.transport.smtp.SmtpTransport;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
@@ -29,6 +30,7 @@ import org.jetbrains.annotations.Nullable;
 public class ImapBackend implements Backend {
     private final ImapStore imapStore;
     private final PowerManager powerManager;
+    private final SmtpTransport smtpTransport;
     private final ImapSync imapSync;
     private final CommandGetFolders commandGetFolders;
     private final CommandSetFlag commandSetFlag;
@@ -43,9 +45,10 @@ public class ImapBackend implements Backend {
 
 
     public ImapBackend(String accountName, BackendStorage backendStorage, ImapStore imapStore,
-            PowerManager powerManager) {
+            PowerManager powerManager, SmtpTransport smtpTransport) {
         this.imapStore = imapStore;
         this.powerManager = powerManager;
+        this.smtpTransport = smtpTransport;
 
         imapSync = new ImapSync(accountName, backendStorage, imapStore);
         commandSetFlag = new CommandSetFlag(imapStore);
@@ -197,4 +200,9 @@ public class ImapBackend implements Backend {
     public void checkServerSettings() throws MessagingException {
         imapStore.checkSettings();
     }
+
+    @Override
+    public void sendMessage(@NotNull Message message) throws MessagingException {
+        smtpTransport.sendMessage(message);
+    }
 }
diff --git a/backend/pop3/build.gradle b/backend/pop3/build.gradle
index aebdf2638..b9da24d5e 100644
--- a/backend/pop3/build.gradle
+++ b/backend/pop3/build.gradle
@@ -13,6 +13,7 @@ dependencies {
 
     api project(":backend:api")
     implementation project(":mail:protocols:pop3")
+    implementation project(":mail:protocols:smtp")
 
     implementation "com.jakewharton.timber:timber:${versions.timber}"
 
diff --git a/backend/pop3/src/main/java/com/fsck/k9/backend/pop3/Pop3Backend.kt b/backend/pop3/src/main/java/com/fsck/k9/backend/pop3/Pop3Backend.kt
index 26f6fb779..377d5e7aa 100644
--- a/backend/pop3/src/main/java/com/fsck/k9/backend/pop3/Pop3Backend.kt
+++ b/backend/pop3/src/main/java/com/fsck/k9/backend/pop3/Pop3Backend.kt
@@ -14,8 +14,14 @@ import com.fsck.k9.mail.Part
 import com.fsck.k9.mail.PushReceiver
 import com.fsck.k9.mail.Pusher
 import com.fsck.k9.mail.store.pop3.Pop3Store
+import com.fsck.k9.mail.transport.smtp.SmtpTransport
 
-class Pop3Backend(accountName: String, backendStorage: BackendStorage, private val pop3Store: Pop3Store) : Backend {
+class Pop3Backend(
+        accountName: String,
+        backendStorage: BackendStorage,
+        private val pop3Store: Pop3Store,
+        private val smtpTransport: SmtpTransport
+) : Backend {
     private val pop3Sync: Pop3Sync = Pop3Sync(accountName, backendStorage, pop3Store)
     private val commandGetFolders = CommandGetFolders()
     private val commandSetFlag = CommandSetFlag(pop3Store)
@@ -110,4 +116,8 @@ class Pop3Backend(accountName: String, backendStorage: BackendStorage, private v
     override fun checkServerSettings() {
         pop3Store.checkSettings()
     }
+
+    override fun sendMessage(message: Message) {
+        smtpTransport.sendMessage(message)
+    }
 }
diff --git a/backend/webdav/src/main/java/com/fsck/k9/backend/webdav/WebDavBackend.kt b/backend/webdav/src/main/java/com/fsck/k9/backend/webdav/WebDavBackend.kt
index 6cf478164..e1ea4e0ff 100644
--- a/backend/webdav/src/main/java/com/fsck/k9/backend/webdav/WebDavBackend.kt
+++ b/backend/webdav/src/main/java/com/fsck/k9/backend/webdav/WebDavBackend.kt
@@ -15,11 +15,13 @@ import com.fsck.k9.mail.Part
 import com.fsck.k9.mail.PushReceiver
 import com.fsck.k9.mail.Pusher
 import com.fsck.k9.mail.store.webdav.WebDavStore
+import com.fsck.k9.mail.transport.WebDavTransport
 
 class WebDavBackend(
         accountName: String,
         backendStorage: BackendStorage,
-        private val webDavStore: WebDavStore
+        private val webDavStore: WebDavStore,
+        private val webDavTransport: WebDavTransport
 ) : Backend {
     private val webDavSync: WebDavSync = WebDavSync(accountName, backendStorage, webDavStore)
     private val commandGetFolders = CommandGetFolders(webDavStore)
@@ -119,4 +121,8 @@ class WebDavBackend(
     override fun checkServerSettings() {
         webDavStore.checkSettings()
     }
+
+    override fun sendMessage(message: Message) {
+        webDavTransport.sendMessage(message)
+    }
 }