Figure 4.5 shows offline email system network protocol layout. When email is sent, a message was sent from the sender mail server Mail Transport Agent (MTA). Both MTA side communicates using Simple Mail Transfer Protocol (SMTP) Server. The recipient MTA delivers the email to the Mail Delivery Agent (MDA) which stores the email as it wait for the user to accept it. Internet Message Access Protocol (IMAP) used for retrieving email on MDA.
Figure 4.5: Offline Email System Network Protocol layout
MDA is protected by login system where it needs a username and password. Email is retrieved by using Mail User Agent (MUA) where it is called an email client on the user device. Webmail is used for this thesis work. If the email destination is not in the local network, the email delivery is pending and the data remain in the mail server storage until it is transferred to the infomediary device. This operation matches the bundle protocol (BP) where the data being stored temporarily and later forwarded to next destination. When the infomediary device establishes a network connection with the offline mail server, the mail database synchronization application will transfer the email data from offline mail server to infomediary device and retrieve new email data from infomediary device to the offline mail server. The new email data from infomediary device which is received from online mail server will be in the new pending email delivery where it is being sent immediately since the destination was in the network until it reaches the user to accept it. The Dynamic Host Configuration Protocol (DHCP) is a network protocol used to configure devices that are connected to a network. The SSID and security codes for the access points are chosen by the administrators. This offline email system used static IP addresses. Both the online and offline server computers are configured as DHCP servers. This enables the servers to allocate IP addresses to any DHCP client.
Figure 4.6 shows online email system network protocol layout. The process is the same as when the infomediary device establishes a network connection with online mail server, the mail database synchronization application will retrieve email data from infomediary device to online mail server and transfer the new email data from online mail server to the infomediary device to be sent to the offline mail server. The email data from infomediary device which is received from the offline mail server will be in pending delivery where the delivery is executed immediately because of the destination is available in the network until it reaches the user to accept it.
Figure 4.6: Online Email System Network Protocol layout