dovecot: migrate to settings option

default.nix

@@ -654,11 +654,8 @@ in
     };
 
     lmtpSaveToDetailMailbox = mkOption {
-      type = types.enum [
-        "yes"
-        "no"
-      ];
-      default = "yes";
+      type = types.bool;
+      default = true;
       description = ''
         If an email address is delimited by a "+", should it be filed into a
         mailbox matching the string after the "+"?  For example,
@@ -882,25 +879,31 @@ in
 
     mailboxes = mkOption {
       description = ''
-        The mailboxes for dovecot.
+        The default mailboxes for Dovecot maildirs.
+
+        The [`special_use`] option must refer to an [RFC6154 2] attribute and lead with an escaped backslash.
+
         Depending on the mail client used it might be necessary to change some mailbox's name.
+
+        [special_use]: https://doc.dovecot.org/2.3/configuration_manual/namespace/#core_setting-namespace/mailbox/special_use
+        [RFC6154 2]: https://datatracker.ietf.org/doc/html/rfc6154.html#section-2
       '';
       default = {
         Trash = {
           auto = "no";
-          specialUse = "Trash";
+          special_use = "\\Trash";
         };
         Junk = {
           auto = "subscribe";
-          specialUse = "Junk";
+          special_use = "\\Junk";
         };
         Drafts = {
           auto = "subscribe";
-          specialUse = "Drafts";
+          special_use = "\\Drafts";
         };
         Sent = {
           auto = "subscribe";
-          specialUse = "Sent";
+          special_use = "\\Sent";
         };
       };
     };