diff --git a/README.md b/README.md
index 6f996be..757aae8 100644
--- a/README.md
+++ b/README.md
@@ -160,7 +160,7 @@ bundle exec bin/mail_mcp generate \
 | `list_mailboxes`            | —                                                                                   | List all IMAP folders                                                                            |
 | `list_mail_messages`        | `folder`, `page`, `per_page`                                                        | List messages with pagination                                                                    |
 | `get_mail_message`          | `folder`, `uid`                                                                     | Fetch full message; attachments uploaded to S3 and returned as presigned URLs                    |
-| `search_mail_messages`      | `folder`, `query`                                                                   | Raw IMAP SEARCH criteria, e.g. `UNSEEN` or `FROM alice@example.com SINCE 01-Jan-2025`            |
+| `search_mail_messages`      | `folder`, `query`                                                                   | Raw IMAP SEARCH criteria, e.g. `UNSEEN` or `FROM alice@example.com SINCE 01-Jan-2025`; returns UIDs            |
 | `send_mail_message`         | `to`, `subject`, `text_body`, `cc`, `bcc`, `html_body`, `attachment_urls`, `folder` | Send via SMTP and append to the Sent folder via IMAP; attachments fetched from S3 presigned URLs |
 | `create_draft_mail_message` | `to`, `subject`, `text_body`, `cc`, `bcc`, `html_body`, `attachment_urls`, `folder` | Append to Drafts via IMAP APPEND; attachments fetched from S3 presigned URLs                     |
 | `delete_mail_message`       | `folder`, `uid`                                                                     | Mark `\Deleted` + EXPUNGE                                                                        |
diff --git a/lib/mail_mcp/imap_client.rb b/lib/mail_mcp/imap_client.rb
index 9b12886..d145741 100644
--- a/lib/mail_mcp/imap_client.rb
+++ b/lib/mail_mcp/imap_client.rb
@@ -90,7 +90,10 @@ def get_message(folder:, uid:)
     def search_messages(folder:, query:)
       MailMCP.logger.info { "IMAP search_messages folder=#{folder.inspect} query=#{query.inspect}" }
       @imap.examine(folder)
-      results = @imap.search(query.split)
+      # UID SEARCH, not SEARCH: the ids returned here are fed back into
+      # get_message/delete_message/move_message/update_flags, which all issue
+      # UID commands. Sequence numbers would only match until the first expunge.
+      results = @imap.uid_search(query.split)
       MailMCP.logger.debug { "IMAP search_messages matched=#{results.size}" }
       results
     end
diff --git a/lib/mail_mcp/tools/search_mail_messages_tool.rb b/lib/mail_mcp/tools/search_mail_messages_tool.rb
index 1eeaa4d..59af44a 100644
--- a/lib/mail_mcp/tools/search_mail_messages_tool.rb
+++ b/lib/mail_mcp/tools/search_mail_messages_tool.rb
@@ -1,7 +1,8 @@
 module MailMCP
   class SearchMailMessagesTool < Tool
     tool_name "search_mail_messages"
-    description "Search messages in an IMAP folder using raw IMAP SEARCH criteria"
+    description "Search messages in an IMAP folder using raw IMAP SEARCH criteria. " \
+                "Returns message UIDs usable with get_mail_message"
     annotations(
       title: "Search Mail Messages",
       read_only_hint: true,
diff --git a/spec/mail_mcp/imap_client_spec.rb b/spec/mail_mcp/imap_client_spec.rb
index d2b3985..6837bcc 100644
--- a/spec/mail_mcp/imap_client_spec.rb
+++ b/spec/mail_mcp/imap_client_spec.rb
@@ -108,15 +108,15 @@
   end
 
   describe "#search_messages" do
-    it "passes raw query string to IMAP SEARCH" do
-      allow(imap).to receive(:search).with(["UNSEEN"]).and_return([1, 2, 3])
+    it "passes raw query string to IMAP UID SEARCH" do
+      allow(imap).to receive(:uid_search).with(["UNSEEN"]).and_return([1, 2, 3])
       client = described_class.new(imap)
       result = client.search_messages(folder: "INBOX", query: "UNSEEN")
       expect(result).to eq([1, 2, 3])
     end
 
     it "supports multi-word criteria" do
-      allow(imap).to receive(:search).with(["FROM", "alice@example.com"]).and_return([5])
+      allow(imap).to receive(:uid_search).with(["FROM", "alice@example.com"]).and_return([5])
       client = described_class.new(imap)
       result = client.search_messages(folder: "INBOX", query: "FROM alice@example.com")
       expect(result).to eq([5])