diff --git a/deltachat-ffi/deltachat.h b/deltachat-ffi/deltachat.h
index f15e75c92..fb5a2e12a 100644
--- a/deltachat-ffi/deltachat.h
+++ b/deltachat-ffi/deltachat.h
@@ -487,6 +487,7 @@ char*           dc_get_blobdir               (const dc_context_t* context);
  *                       0 = Everybody (except explicitly blocked contacts),
  *                       1 = Contacts (default, does not include contact requests),
  *                       2 = Nobody (calls never result in a notification).
+ * - `force_encryption` = 1 (default) to force encryption, 0 to allow unencrypted messages.
  *
  * Also, there are configs that are only needed
  * if you want to use the deprecated dc_configure() API, such as:
diff --git a/deltachat-rpc-client/tests/test_chatlist_events.py b/deltachat-rpc-client/tests/test_chatlist_events.py
index f13769e07..a6152049d 100644
--- a/deltachat-rpc-client/tests/test_chatlist_events.py
+++ b/deltachat-rpc-client/tests/test_chatlist_events.py
@@ -87,6 +87,7 @@ def test_delivery_status_failed(acfactory: ACFactory) -> None:
     Test change status on chatlistitem when status changes failed
     """
     (alice,) = acfactory.get_online_accounts(1)
+    alice.set_config("force_encryption", "0")
 
     invalid_contact = alice.create_contact("example@example.com", "invalid address")
     invalid_chat = alice.get_chat_by_id(alice._rpc.create_chat_by_contact_id(alice.id, invalid_contact.id))
diff --git a/src/chat.rs b/src/chat.rs
index 8f1b82bdd..ab9810205 100644
--- a/src/chat.rs
+++ b/src/chat.rs
@@ -2823,7 +2823,12 @@ pub(crate) async fn create_send_msg_jobs(context: &Context, msg: &mut Message) -
             .await?;
     }
 
-    let needs_encryption = msg.param.get_bool(Param::GuaranteeE2ee).unwrap_or_default();
+    let needs_encryption = msg.param.get_bool(Param::GuaranteeE2ee).unwrap_or_default()
+        || (!msg
+            .param
+            .get_bool(Param::ForcePlaintext)
+            .unwrap_or_default()
+            && context.get_config_bool(Config::ForceEncryption).await?);
     let mimefactory = match MimeFactory::from_msg(context, msg.clone()).await {
         Ok(mf) => mf,
         Err(err) => {
diff --git a/src/config.rs b/src/config.rs
index f0ca2fafb..accf04724 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -486,6 +486,12 @@ pub enum Config {
     /// Experimental option denoting that the current profile is shared between multiple team members.
     /// For now, the only effect of this option is that seen flags are not synchronized.
     TeamProfile,
+
+    /// Process unencrypted messages.
+    ///
+    /// Unencrypted messages are fetched and processed only if this setting is explicitly enabled.
+    #[strum(props(default = "1"))]
+    ForceEncryption,
 }
 
 impl Config {
@@ -501,7 +507,11 @@ impl Config {
     pub(crate) fn is_synced(&self) -> bool {
         matches!(
             self,
-            Self::Displayname | Self::MdnsEnabled | Self::Selfavatar | Self::Selfstatus,
+            Self::Displayname
+                | Self::MdnsEnabled
+                | Self::Selfavatar
+                | Self::Selfstatus
+                | Self::ForceEncryption,
         )
     }
 
diff --git a/src/context.rs b/src/context.rs
index f8128e1af..9cd63c654 100644
--- a/src/context.rs
+++ b/src/context.rs
@@ -1053,6 +1053,12 @@ impl Context {
             "team_profile",
             self.get_config_bool(Config::TeamProfile).await?.to_string(),
         );
+        res.insert(
+            "force_encryption",
+            self.get_config_bool(Config::ForceEncryption)
+                .await?
+                .to_string(),
+        );
 
         let elapsed = time_elapsed(&self.creation_time);
         res.insert("uptime", duration_to_str(elapsed));
diff --git a/src/e2ee.rs b/src/e2ee.rs
index 45edc4d6b..e49804906 100644
--- a/src/e2ee.rs
+++ b/src/e2ee.rs
@@ -109,6 +109,7 @@ pub async fn ensure_secret_key_exists(context: &Context) -> Result<()> {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::chat;
     use crate::chat::send_text_msg;
     use crate::config::Config;
     use crate::message::Message;
@@ -155,6 +156,19 @@ Sent with my Delta Chat Messenger: https://delta.chat";
         );
     }
 
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_cannot_send_unencrypted_by_default() -> Result<()> {
+        let mut tcm = TestContextManager::new();
+        let alice = &tcm.alice().await;
+        let bob = &tcm.bob().await;
+        let chat = alice.create_email_chat(bob).await;
+
+        let mut msg = Message::new_text("Hello!".to_string());
+        assert!(chat::send_msg(alice, chat.id, &mut msg).await.is_err());
+
+        Ok(())
+    }
+
     #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
     async fn test_chatmail_can_send_unencrypted() -> Result<()> {
         let mut tcm = TestContextManager::new();
diff --git a/src/imap.rs b/src/imap.rs
index bedc0376c..d6cabae0e 100644
--- a/src/imap.rs
+++ b/src/imap.rs
@@ -1994,12 +1994,21 @@ pub(crate) async fn prefetch_should_download(
     // prevent_rename=true as this might be a mailing list message and in this case it would be bad if we rename the contact.
     // (prevent_rename is the last argument of from_field_to_contact_id())
 
+    let is_encrypted = if let Some(content_type) = headers.get_header_value(HeaderDef::ContentType)
+    {
+        mailparse::parse_content_type(&content_type).mimetype == "multipart/encrypted"
+    } else {
+        false
+    };
+
     if flags.any(|f| f == Flag::Draft) {
         info!(context, "Ignoring draft message");
         return Ok(false);
     }
 
-    let should_download = !blocked_contact || maybe_ndn;
+    let should_download = maybe_ndn
+        || (!blocked_contact
+            && (is_encrypted || !context.get_config_bool(Config::ForceEncryption).await?));
     Ok(should_download)
 }
 
diff --git a/src/imap/session.rs b/src/imap/session.rs
index 8d4e7e087..e1e397574 100644
--- a/src/imap/session.rs
+++ b/src/imap/session.rs
@@ -21,6 +21,7 @@ const PREFETCH_FLAGS: &str = "(UID RFC822.SIZE BODY.PEEK[HEADER.FIELDS (\
                               DATE \
                               X-MICROSOFT-ORIGINAL-MESSAGE-ID \
                               FROM \
+                              CONTENT-TYPE \
                               CHAT-VERSION \
                               CHAT-IS-POST-MESSAGE \
                               AUTOCRYPT-SETUP-MESSAGE\
diff --git a/src/receive_imf.rs b/src/receive_imf.rs
index 62db19810..5cb90a257 100644
--- a/src/receive_imf.rs
+++ b/src/receive_imf.rs
@@ -505,6 +505,14 @@ pub(crate) async fn receive_imf_inner(
         Ok(mime_parser) => mime_parser,
     };
 
+    if !mime_parser.was_encrypted()
+        && mime_parser.get_header(HeaderDef::SecureJoin).is_none()
+        && context.get_config_bool(Config::ForceEncryption).await?
+    {
+        warn!(context, "Fetched unencrypted message, ignoring");
+        return trash().await;
+    }
+
     let rfc724_mid_orig = &mime_parser
         .get_rfc724_mid()
         .unwrap_or(rfc724_mid.to_string());
diff --git a/src/receive_imf/receive_imf_tests.rs b/src/receive_imf/receive_imf_tests.rs
index 4de21b2c0..e32bd9897 100644
--- a/src/receive_imf/receive_imf_tests.rs
+++ b/src/receive_imf/receive_imf_tests.rs
@@ -4498,12 +4498,12 @@ async fn test_outgoing_msg_forgery() -> Result<()> {
     imex(alice, ImexMode::ExportSelfKeys, export_dir.path(), None).await?;
     // We need Bob only to encrypt the forged message to Alice's key, actually Bob doesn't
     // participate in the scenario.
-    let bob = &TestContext::new().await;
+    let bob = &tcm.unconfigured().await;
     assert_eq!(crate::key::load_self_secret_keyring(bob).await?.len(), 0);
     bob.configure_addr("bob@example.net").await;
     imex(bob, ImexMode::ImportSelfKeys, export_dir.path(), None).await?;
     assert_eq!(crate::key::load_self_secret_keyring(bob).await?.len(), 1);
-    let malice = &TestContext::new().await;
+    let malice = &tcm.unconfigured().await;
     malice.configure_addr(alice_addr).await;
 
     let malice_chat_id = tcm
@@ -4513,9 +4513,8 @@ async fn test_outgoing_msg_forgery() -> Result<()> {
     assert_eq!(crate::key::load_self_secret_keyring(bob).await?.len(), 1);
 
     let sent_msg = malice.send_text(malice_chat_id, "hi from malice").await;
-    let msg = alice.recv_msg(&sent_msg).await;
-    assert_eq!(msg.state, MessageState::OutDelivered);
-    assert!(!msg.get_showpadlock());
+    let msg = alice.recv_msg_opt(&sent_msg).await;
+    assert!(msg.is_none());
 
     Ok(())
 }
diff --git a/src/sync.rs b/src/sync.rs
index 8b050456d..3f386bdea 100644
--- a/src/sync.rs
+++ b/src/sync.rs
@@ -810,4 +810,23 @@ mod tests {
         assert_eq!(msg.text, "Member Me added by alice@example.org.");
         Ok(())
     }
+
+    /// Tests that "force encryption" setting is synced.
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_sync_force_encryption() -> Result<()> {
+        let mut tcm = TestContextManager::new();
+        let alice = &tcm.alice().await;
+        let alice2 = &tcm.alice().await;
+        alice.set_config_bool(Config::SyncMsgs, true).await?;
+        alice2.set_config_bool(Config::SyncMsgs, true).await?;
+
+        assert_eq!(alice.get_config_bool(Config::ForceEncryption).await?, true);
+        alice2
+            .set_config_bool(Config::ForceEncryption, false)
+            .await?;
+        test_utils::sync(alice2, alice).await;
+        assert_eq!(alice.get_config_bool(Config::ForceEncryption).await?, false);
+
+        Ok(())
+    }
 }
diff --git a/src/test_utils.rs b/src/test_utils.rs
index 13493b162..8e8106ca2 100644
--- a/src/test_utils.rs
+++ b/src/test_utils.rs
@@ -1231,9 +1231,8 @@ ORDER BY id"
     }
 
     /// Allow reception of unencrypted messages.
-    #[expect(clippy::unused_async)]
     pub async fn allow_unencrypted(&self) -> Result<()> {
-        // Does nothing for now.
+        self.set_config_bool(Config::ForceEncryption, false).await?;
         Ok(())
     }
 }