--- a/src/mail/ngx_mail.h
+++ b/src/mail/ngx_mail.h
@@ -116,6 +116,7 @@ typedef struct {
     ngx_msec_t              resolver_timeout;
 
     ngx_uint_t              max_errors;
+    ngx_uint_t              max_commands;
 
     ngx_str_t               server_name;
 
@@ -234,6 +235,7 @@ typedef struct {
     ngx_array_t             args;
 
     ngx_uint_t              errors;
+    ngx_uint_t              commands;
     ngx_uint_t              login_attempt;
 
     /* used to parse POP3/IMAP/SMTP command */

--- a/src/mail/ngx_mail_core_module.c
+++ b/src/mail/ngx_mail_core_module.c
@@ -92,6 +92,13 @@ static ngx_command_t  ngx_mail_core_comm
       offsetof(ngx_mail_core_srv_conf_t, max_errors),
       NULL },
 
+    { ngx_string("max_commands"),
+      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
+      ngx_conf_set_num_slot,
+      NGX_MAIL_SRV_CONF_OFFSET,
+      offsetof(ngx_mail_core_srv_conf_t, max_commands),
+      NULL },
+
       ngx_null_command
 };
 
@@ -171,6 +178,7 @@ ngx_mail_core_create_srv_conf(ngx_conf_t
     cscf->resolver_timeout = NGX_CONF_UNSET_MSEC;
 
     cscf->max_errors = NGX_CONF_UNSET_UINT;
+    cscf->max_commands = NGX_CONF_UNSET_UINT;
 
     cscf->resolver = NGX_CONF_UNSET_PTR;
 
@@ -192,6 +200,7 @@ ngx_mail_core_merge_srv_conf(ngx_conf_t 
                               30000);
 
     ngx_conf_merge_uint_value(conf->max_errors, prev->max_errors, 5);
+    ngx_conf_merge_uint_value(conf->max_commands, prev->max_commands, 1000);
 
     ngx_conf_merge_str_value(conf->server_name, prev->server_name, "");
 

--- a/src/mail/ngx_mail_handler.c
+++ b/src/mail/ngx_mail_handler.c
@@ -896,6 +896,18 @@ ngx_mail_read_command(ngx_mail_session_t
         return NGX_ERROR;
     }
 
+    s->commands++;
+
+    if (s->commands > cscf->max_commands) {
+
+        ngx_log_error(NGX_LOG_INFO, c->log, 0,
+                      "client sent too many commands");
+
+        s->quit = 1;
+
+        return NGX_MAIL_PARSE_INVALID_COMMAND;
+    }
+
     return NGX_OK;
 }