具延展性透明之中小企業電子郵件委外服務:設計與測試

Abstract

本論文提出一具延展性透明且針企業的電子郵件委外服務。目前絕大部分的企業都自行操作其電子郵件伺服器，不良的管理時常導致故障，因此，有強烈的需求將其電子郵件伺服器外包，然而，大部分免費的電子郵件服務如Hotmail.com和Yahoo!mail ，主要以個人用戶而非企業用戶為目標。本系統的特色有線上透明電子郵件委外服務，友善集中式的前端與後端管理，豐富的服務，如anti-virus與web mail，及可延展至數百萬個帳號與上萬個公司域名。此系統由一可延展且可靠Open source SMTP, POP3/IMAP, LDAP, relay and anti-virus伺服器所建構的叢集系統驅動。經由內部測試，辨別系統瓶頸且採取解決方案有如分散mail queue到多顆硬碟、限制queue目錄的大小、搬移一部份的metadata到快速目錄搜尋的Reiser檔案系統。展示經調整的系統在9個節點的叢集系統下可達到每秒1000封信的效能，而另一個系統需要約20個節點才能達到相同的效能。

This work presents a scalable transparent e-mail outsourcing service for enterprises. At present, most enterprises operate their own mail servers, where poor management often leads to malfunctioning. Thus, there is a strong need to outsource their e-mail servers. However, most free e-mail services, such as hotmail.com and Yahoo!mail, target at individuals instead of enterprises. Our system features transparent on-line outsourcing, friendly centralized front-end and back-end management, and a rich set of services, such as anti-virus and web mail, and can scale to millions of accounts and tens of thousands of enterprise domains. The system is driven by a scalable and reliable server cluster built from open source SMTP, POP3/IMAP, LDAP, relay, anti-virus, and mail data servers. Through internal benchmark, we identify bottlenecks and apply resolutions such as splitting the mail queue to multiple disks, limiting the size of queue directory, and moving some metadata to the Reiser file system which has fast directory lookup. We demonstrate that the tuned system can achieve 1000 messages per second under a 14-node cluster, outperforming another reported system which requires a 20-node cluster to achieve the same throughput.