diff --git a/src/eimap.erl b/src/eimap.erl
--- a/src/eimap.erl
+++ b/src/eimap.erl
@@ -146,6 +146,21 @@
 disconnected(Command, State) when is_record(Command, command) ->
     { next_state, disconnected, enque_command(Command, State) }.
 
+
+%Throttle if the target process is getting overloaded.
+%This allows the socket buffers to fill up eventually,
+%so regular congestion control can kick in.
+throttle(Receiver, Limit) ->
+    {_, MessageQueueLength} = process_info(Receiver, message_queue_len),
+    if
+        MessageQueueLength > Limit ->
+            SleepDuration = trunc(MessageQueueLength / 2),
+            lager:debug("Throttling for ~p with queue length ~p", [SleepDuration, MessageQueueLength]),
+            timer:sleep(SleepDuration),
+            throttle(Receiver, Limit);
+        true -> false
+    end.
+
 passthrough(flush_passthrough_buffer, #state{ passthrough_send_buffer = Buffer } = State) ->
     %lager:info("Passing through ~p", [Buffer]),
     passthrough({ passthrough, Buffer }, State#state{ passthrough_send_buffer = <<>> });
@@ -159,6 +174,8 @@
     { next_state, passthrough, State };
 passthrough({ data, Data }, #state{ passthrough_recv = Receiver } = State) ->
     %lager:info("Passing back ~p", [Data]),
+
+    throttle(Receiver, 100),
     Receiver ! { imap_server_response, Data },
     { next_state, passthrough, State };
 passthrough(Command, State) when is_record(Command, command) ->