Make LMTP memory limit configurable

default.nix

@@ -460,6 +460,14 @@ in
       '';
     };
 
+    lmtpMemoryLimit = mkOption {
+      type = types.int;
+      default = 256;
+      description = ''
+        The memory limit for the LMTP service, in megabytes.
+      '';
+    };
+
     extraVirtualAliases = mkOption {
       type = let
         loginAccount = mkOptionType {

mail-server/dovecot.nix

@@ -291,6 +291,7 @@ in
             mode = 0600
             user = ${postfixCfg.user}
           }
+	  vsz_limit = ${builtins.toString cfg.lmtpMemoryLimit} MB
         }
 
         recipient_delimiter = ${cfg.recipientDelimiter}