MaxBulk Mailer works exactly the same way as any other e-mail software. It uses a defined protocol to connect and to talk with an outgoing e-mail server over the internet. The protocol is like a language both MaxBulk Mailer and the server understand. It is called SMTP. SMTP stands for Simple Mail Transport Protocol. You always have access to at least one SMTP server through your ISP (Internet Service Provider).
When you press the MaxBulk Mailer 'Send' button, your messages are sent to your ISP outgoing e-mail SMTP server. You can follow the process looking at the Delivery panel. You can see how MaxBulk Mailer connects, authenticates, sends your messages and wait for delivery receipts. During that process MaxBulk Mailer marks recipients as delivered only when the server responds with a successful delivery receipt. That receipt uses to include a reference ID for tracking.
Once the server accepts your messages for delivery, it becomes the unique responsible for routing them all properly till their final destination. In other words, the server tells MaxBulk Mailer the messages are valid and are accepted for delivery. At this point MaxBulk Mailer is done.
Your SMTP server then looks at who the message is to. Specifically it examines the domain it is supposed to get delivered to. This domain is then looked up via an online directory of sorts known as DNS (Domain Name Service) to determine which server handles its incoming e-mail. This special DNS host is known as the MX (mail exchange) record and the server as the Mail Exchanger, receiving mail server or incoming SMTP server.
If your SMTP server is unable to look up the destination e-mail address, a bounce is generated else it will connect to that Mail Exchanger and will attempt to deliver the messages. Usually this is where the first level of anti-spam filter software is used. Most commonly one or more real-time blacklists are used to block messages from anyone who's not to be trusted. If an error occurs a bounce is generated. Note that a blacklisting is also supposed to generate a bounce but is is not always the case.
Frequently users will also have an e-mail spam blocker deployed client-side. Increasingly some email clients have simple spam e-mail stopper technology included. This presents one more barrier an e-mail has to pass through before making it to the user's inbox.