diff --git a/cmd/oo/mails.go b/cmd/oo/mails.go
index 3b90c5a..d6d5b4d 100644
--- a/cmd/oo/mails.go
+++ b/cmd/oo/mails.go
@@ -22,6 +22,7 @@ func init() {
 	mailsCmd.AddCommand(mailsFoldersCmd())
 	mailsCmd.AddCommand(mailsListCmd())
 	mailsCmd.AddCommand(mailsGetCmd())
+	mailsCmd.AddCommand(mailsDownloadAttachmentCmd())
 	mailsCmd.AddCommand(mailsDraftCmd())
 	mailsCmd.AddCommand(mailsAttachCmd())
 	mailsCmd.AddCommand(mailsDraftInvoiceCmd())
@@ -131,6 +132,48 @@ func mailsGetCmd() *cobra.Command {
 	}
 }
 
+func mailsDownloadAttachmentCmd() *cobra.Command {
+	var outPath string
+	cmd := &cobra.Command{
+		Use:   "download-attachment ATTACHMENT_ID",
+		Short: "Download a mail attachment by attachment id",
+		Long: `Download a raw attachment from OnlyOffice Mail's download.ashx handler.
+
+Example:
+  oo mails download-attachment 12345 --out /tmp/attach.bin
+`,
+		Args: cobra.ExactArgs(1),
+		RunE: func(cmd *cobra.Command, args []string) error {
+			if strings.TrimSpace(outPath) == "" {
+				return fmt.Errorf("--out is required")
+			}
+			c, err := newOO(cmd)
+			if err != nil {
+				return err
+			}
+			body, err := c.DownloadMailAttachment(cmd.Context(), args[0])
+			if err != nil {
+				return err
+			}
+			if err := writeMailAttachment(outPath, body); err != nil {
+				return err
+			}
+			if outputFormat == "json" {
+				printObject(map[string]any{
+					"attachmentId": args[0],
+					"bytes":        len(body),
+					"path":         outPath,
+				})
+				return nil
+			}
+			fmt.Printf("saved %d bytes to %s\n", len(body), outPath)
+			return nil
+		},
+	}
+	cmd.Flags().StringVar(&outPath, "out", "", "output file path")
+	return cmd
+}
+
 func mailsDraftCmd() *cobra.Command {
 	var from, to, cc, bcc, subject, body, html string
 	var id int64
@@ -297,6 +340,13 @@ func formatInvoiceCostEUR(v any) string {
 	return s
 }
 
+func writeMailAttachment(path string, body []byte) error {
+	if strings.TrimSpace(path) == "" {
+		return fmt.Errorf("attachment output path is required")
+	}
+	return os.WriteFile(path, body, 0o644)
+}
+
 func mailsDeleteCmd() *cobra.Command {
 	return &cobra.Command{
 		Use:     "delete ID [ID...]",
diff --git a/cmd/oo/mails_cli_test.go b/cmd/oo/mails_cli_test.go
new file mode 100644
index 0000000..dd69516
--- /dev/null
+++ b/cmd/oo/mails_cli_test.go
@@ -0,0 +1,28 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestWriteMailAttachment(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "attach.bin")
+	body := []byte("payload")
+	if err := writeMailAttachment(path, body); err != nil {
+		t.Fatalf("writeMailAttachment: %v", err)
+	}
+	got, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("ReadFile: %v", err)
+	}
+	if string(got) != string(body) {
+		t.Fatalf("body = %q", got)
+	}
+}
+
+func TestWriteMailAttachmentRequiresPath(t *testing.T) {
+	if err := writeMailAttachment("", []byte("x")); err == nil {
+		t.Fatal("expected error for empty path")
+	}
+}
diff --git a/cmd/oo/main.go b/cmd/oo/main.go
index 13c38fc..30ba5b6 100644
--- a/cmd/oo/main.go
+++ b/cmd/oo/main.go
@@ -13,7 +13,7 @@
 //	oo cases         list | create | delete | member-add
 //	oo crm-tasks     list | create | delete | categories
 //	oo crm           cleanup
-//	oo mails         accounts | folders | list | get | draft | attach | draft-invoice | delete
+//	oo mails         accounts | folders | list | get | download-attachment | draft | attach | draft-invoice | delete
 //	oo invoices      list | get | create | update | pdf | pdf-cleanup | status | delete | items …
 //
 // CRM association rules: docs/crm-associations.md