Message queue is full

Question: Product seems to stop receiving mail and the Queue directory has loads of files in it. How can I make it continue working?
Answer: First, we need to examine how SMTP server works in general.
If you notice in step 1, you are sending messages to our server. Server will queue this mail and store it as a file on disk. After that, in step 2, server will send your message from the queue, to Internet.
If the speed of your OUTGOING (not to be confused with incoming) Internet connection is slow and you send lots of messages to the server, naturally all the messages will be queued, but the sending will be slower and slower, depending on your connection and how many connections can be opened and how fast the target server will accept your messages for delivery.
If you are sending mass mailings and you have a regular home DSL or Cable Internet connection, you can expect to overload your server very quickly, because your outgoing speed of connection is very slow for sending so many messages through. It is normally not higher than 600Kbps in most cases (remember, you need to look at the outgoing speed and not on your incoming speed, because you are sending and not receiving messages). The server has a limit for your queue (it is specified in the settings of the server) and also limit for each individual message (that is also specified in the settings).
That is why the server can accept your messages much faster then it can send.
What you need to do is slow down the sending of the messages or increase the limit of the queue in the settings.
You can easily do it in the throttling settings of our SMTP server, then you will be loading our server proportionally. Not faster than it can actually send out those message through the Internet