diff --git a/default.nix b/default.nix
index 499e0aa..efc82e9 100644
--- a/default.nix
+++ b/default.nix
@@ -182,6 +182,16 @@ in
       default = {};
     };
 
+    lmptSaveToDetailMailbox = mkOption {
+      type = types.enum ["yes" "no"];
+      default = "yes";
+      description = ''
+        If an email address is delimited by a "+", should it be filed into a
+        mailbox matching the string after the "+"?  For example,
+        user1+test@example.com would be filed into the mailbox "test".
+      '';
+    };
+
     extraVirtualAliases = mkOption {
       type = types.loaOf (mkOptionType {
         name = "Login Account";
diff --git a/mail-server/dovecot.nix b/mail-server/dovecot.nix
index f0a370a..ca05ade 100644
--- a/mail-server/dovecot.nix
+++ b/mail-server/dovecot.nix
@@ -139,7 +139,7 @@ in
         }
 
         recipient_delimiter = +
-        lmtp_save_to_detail_mailbox = yes
+        lmtp_save_to_detail_mailbox = ${cfg.lmptSaveToDetailMailbox}
 
         protocol lmtp {
           mail_plugins = $mail_plugins sieve