E-Mail over low bandwidth networks

Abstract

Many Sri Lankans still use low bandwidth connections (e.g. dial-up, GPRS) to internet due to the high cost and limited geographical coverage of broadband internet (e.g. ADSL, 3G) services. Email access over this type of network is painful due to the large amount of time taken to download messages, especially when emails with large attachments and images are received. Bandwidth is also wasted for downloading spam and less important emails./ The objective of this research is to minimize the delays of reading email over a low bandwidth link. It also aims to reduce the load on the low bandwidth connection, thereby improving the performance for other users and applications. This thesis presents a proxy based solution for accessing email using the IMAP protocol, thereby minimizing changes to the email server and client. Two IMAP proxy servers are installed between the mail server and the client, upstream and downstream of the low-bandwidth link./ A user defines priorities for email, and specifies whether all, part or none of each incoming message should be pre-fetched to the local email client. The upstream IMAP Proxy processes the IMAP responses according to the set priorities, compresses them using glib library and sends them to the downstream IMAP proxy which is in the client computer. The downstream IMAP proxy in turn decompresses the emails and sends them to the email client. Finally, the mailbox of the email client is populated according to the priorities set by the user. In this process instead of downloading all full emails to the client, a mix comprising of full emails, the lisle KB of emails and headers only are downloaded saving bandwidth. Bandwidth is further saved by compressing image files. A GUI application is provided for the user to configure the filter rules.