diff --git a/src/imap/command/examined.rs b/src/imap/command/examined.rs
index ef5cecc..bb05250 100644
--- a/src/imap/command/examined.rs
+++ b/src/imap/command/examined.rs
@@ -120,7 +120,10 @@ impl<'a> ExaminedContext<'a> {
         criteria: &SearchKey<'a>,
         uid: &bool,
     ) -> Result<(Response<'static>, flow::Transition)> {
-        let found = self.mailbox.search(charset, criteria, *uid).await?;
+        let (found, enable_condstore) = self.mailbox.search(charset, criteria, *uid).await?;
+        if enable_condstore {
+            self.client_capabilities.enable_condstore();
+        }
         Ok((
             Response::build()
                 .to_req(self.req)
diff --git a/src/imap/command/selected.rs b/src/imap/command/selected.rs
index 24e1f41..de59ed3 100644
--- a/src/imap/command/selected.rs
+++ b/src/imap/command/selected.rs
@@ -146,7 +146,10 @@ impl<'a> SelectedContext<'a> {
         criteria: &SearchKey<'a>,
         uid: &bool,
     ) -> Result<(Response<'static>, flow::Transition)> {
-        let found = self.mailbox.search(charset, criteria, *uid).await?;
+        let (found, enable_condstore) = self.mailbox.search(charset, criteria, *uid).await?;
+        if enable_condstore {
+            self.client_capabilities.enable_condstore();
+        }
         Ok((
             Response::build()
                 .to_req(self.req)
diff --git a/src/imap/mailbox_view.rs b/src/imap/mailbox_view.rs
index 61beed5..ecdd745 100644
--- a/src/imap/mailbox_view.rs
+++ b/src/imap/mailbox_view.rs
@@ -325,7 +325,7 @@ impl MailboxView {
         _charset: &Option<Charset<'a>>,
         search_key: &SearchKey<'a>,
         uid: bool,
-    ) -> Result<Vec<Body<'static>>> {
+    ) -> Result<(Vec<Body<'static>>, bool)> {
         // 1. Compute the subset of sequence identifiers we need to fetch
         // based on the search query
         let crit = search::Criteria(search_key);
@@ -354,7 +354,10 @@ impl MailboxView {
             _ => final_selection.map(|in_idx| in_idx.i).collect(),
         };
 
-        Ok(vec![Body::Data(Data::Search(selection_fmt))])
+        // 7. Add the modseq entry if needed
+        let is_modseq = crit.is_modseq();
+
+        Ok((vec![Body::Data(Data::Search(selection_fmt))], is_modseq))
     }
 
     // ----
diff --git a/src/imap/search.rs b/src/imap/search.rs
index 12bad51..61cbad5 100644
--- a/src/imap/search.rs
+++ b/src/imap/search.rs
@@ -112,6 +112,17 @@ impl<'a> Criteria<'a> {
         }
     }
 
+    pub fn is_modseq(&self) -> bool {
+        use SearchKey::*;
+        match self.0 {
+            And(and_list) => and_list.as_ref().iter().any(|child| Criteria(child).is_modseq()),
+            Or(left, right) => Criteria(left).is_modseq() || Criteria(right).is_modseq(),
+            Not(child) => Criteria(child).is_modseq(),
+            ModSeq { .. } => true,
+            _ => false,
+        } 
+    }
+
     /// Returns emails that we now for sure we want to keep
     /// but also a second list of emails we need to investigate further by
     /// fetching some remote data