diff --git a/src/chat.rs b/src/chat.rs
index 7f49a4ace..7b0aa53a1 100644
--- a/src/chat.rs
+++ b/src/chat.rs
@@ -1885,10 +1885,11 @@ impl Chat {
     pub async fn is_encrypted(&self, context: &Context) -> Result<bool> {
         let is_encrypted = self.is_protected()
             || match self.typ {
-                Chattype::Single => {
-                    match context
+                Chattype::Group if !self.grpid.is_empty() => true,
+                Chattype::Group | Chattype::Single => {
+                    let contacts = context
                         .sql
-                        .query_row_optional(
+                        .query_map(
                             "SELECT cc.contact_id, c.fingerprint<>''
                              FROM chats_contacts cc LEFT JOIN contacts c
                                  ON c.id=cc.contact_id
@@ -1900,16 +1901,13 @@ impl Chat {
                                 let is_key: bool = row.get(1)?;
                                 Ok((id, is_key))
                             },
+                            |ids| ids.collect::<Result<Vec<_>, _>>().map_err(Into::into),
                         )
-                        .await?
-                    {
-                        Some((id, is_key)) => is_key || id == ContactId::DEVICE,
-                        None => true,
-                    }
-                }
-                Chattype::Group => {
-                    // Do not encrypt ad-hoc groups.
-                    !self.grpid.is_empty()
+                        .await?;
+                    (self.typ != Chattype::Group || contacts.iter().any(|&(_, is_key)| is_key))
+                        && contacts.iter().all(|&(id, is_key)| {
+                            is_key || matches!(id, ContactId::SELF | ContactId::DEVICE)
+                        })
                 }
                 Chattype::Mailinglist => false,
                 Chattype::OutBroadcast | Chattype::InBroadcast => true,
diff --git a/src/receive_imf.rs b/src/receive_imf.rs
index 185a2626d..c2d09ded8 100644
--- a/src/receive_imf.rs
+++ b/src/receive_imf.rs
@@ -114,7 +114,8 @@ enum ChatAssignment {
 
     /// Group chat without a Group ID.
     ///
-    /// This is not encrypted.
+    /// This is either encrypted or unencrypted. Encryption never downgrades, but it can upgrade if
+    /// the last address-contact is removed from the group.
     AdHocGroup,
 
     /// Assign the message to existing chat
@@ -372,25 +373,52 @@ async fn get_to_and_past_contact_ids(
             }
         }
         ChatAssignment::AdHocGroup => {
-            to_ids = add_or_lookup_contacts_by_address_list(
-                context,
-                &mime_parser.recipients,
-                if !mime_parser.incoming {
-                    Origin::OutgoingTo
-                } else if incoming_origin.is_known() {
-                    Origin::IncomingTo
-                } else {
-                    Origin::IncomingUnknownTo
-                },
-            )
-            .await?;
+            let key_to_ids = match mime_parser.was_encrypted() {
+                false => Vec::new(),
+                true => {
+                    let ids = lookup_key_contacts_by_address_list(
+                        context,
+                        &mime_parser.recipients,
+                        to_member_fingerprints,
+                        None,
+                    )
+                    .await?;
+                    match ids.contains(&None) {
+                        false => ids,
+                        true => Vec::new(),
+                    }
+                }
+            };
+            if !key_to_ids.is_empty() {
+                to_ids = key_to_ids;
+                past_ids = lookup_key_contacts_by_address_list(
+                    context,
+                    &mime_parser.past_members,
+                    past_member_fingerprints,
+                    None,
+                )
+                .await?;
+            } else {
+                to_ids = add_or_lookup_contacts_by_address_list(
+                    context,
+                    &mime_parser.recipients,
+                    if !mime_parser.incoming {
+                        Origin::OutgoingTo
+                    } else if incoming_origin.is_known() {
+                        Origin::IncomingTo
+                    } else {
+                        Origin::IncomingUnknownTo
+                    },
+                )
+                .await?;
 
-            past_ids = add_or_lookup_contacts_by_address_list(
-                context,
-                &mime_parser.past_members,
-                Origin::Hidden,
-            )
-            .await?;
+                past_ids = add_or_lookup_contacts_by_address_list(
+                    context,
+                    &mime_parser.past_members,
+                    Origin::Hidden,
+                )
+                .await?;
+            }
         }
         ChatAssignment::OneOneChat => {
             let pgp_to_ids = add_or_lookup_key_contacts(
@@ -2535,7 +2563,7 @@ async fn lookup_or_create_adhoc_group(
             .query_row(
                 "SELECT c.id, c.blocked
                 FROM chats c INNER JOIN msgs m ON c.id=m.chat_id
-                WHERE m.hidden=0 AND c.grpid='' AND c.name=?
+                WHERE m.hidden=0 AND (? OR c.grpid='') AND c.name=?
                 AND (SELECT COUNT(*) FROM chats_contacts
                      WHERE chat_id=c.id
                      AND add_timestamp >= remove_timestamp)=?
@@ -2544,7 +2572,7 @@ async fn lookup_or_create_adhoc_group(
                      AND contact_id NOT IN (SELECT id FROM temp.contacts)
                      AND add_timestamp >= remove_timestamp)=0
                 ORDER BY m.timestamp DESC",
-                (&grpname, contact_ids.len()),
+                (mime_parser.was_encrypted(), &grpname, contact_ids.len()),
                 |row| {
                     let id: ChatId = row.get(0)?;
                     let blocked: Blocked = row.get(1)?;