Bandwidth usage on Mithi Connect Server™

A typical mail server setup consists of a Relay/SMTP server, a central mail server hosting all the mailboxes for the corporate or a distributed setup in which each branch has a dedicated server and are tied together by a central hub server.

The traffic between different servers and clients accessing the servers depend on various factors such as number of users, POP/IMAP/web mail access, and number of services enabled on the servers etc.

The sections below give a summary of the traffic on each type of server.


SMTP/Relay Server

Characteristics of a SMTP/Relay Server

  1. The Relay Server is hosted in the DMZ of the Corporate Data center and is separated from the corporate network by a firewall.
  2. The Relay Server has a public IP.
  3. The Internet access is via the following protocols: SMTP.
  4. The SMTP traffic will be large in the following cases:
    • Incoming and Outgoing traffic is via the same server.
    • Number of users hosted on the server is large.
    • More than one domain is hosted on the same server.
    • The average number of Internet mail to individual mailboxes is high.
    • The average mail size from Internet is high.
    • The server is targeted for a spam or a DOS/DDOS attack.
  5. The function of the Relay server is to scan incoming and send the clean mail to the Hub / Corporate Server. Mail policies, RBL checks and SMTP authentication is also done on this server. Internet servers receive about 30-40 spam and virus and invalid SMTP connections. The rest can be considered valid mail and flows to the Corporate / hub server.
  6. The Relay server can also be configured to relay outgoing mail to the Internet.

Traffic on the connections to the SMTP/Relay Server

Traffic on the Internet connection to the Relay Server

Traffic Cause
SMTP
  1. Legitimate incoming mail
  2. Spam and virus
  3. DOS/DDOS attacks
  4. Outgoing mail

Traffic on the link between the Relay Server and the Hub/Corporate server

Traffic Cause
SMTP
  1. Legitimate incoming mail
  2. Outgoing mail

Front End Server

Characteristics of a Front End Server

  1. The Front End Server is hosted in the DMZ of the Corporate Data center and is separated from the corporate network by a firewall.
  2. The Front End Server has a public IP.
  3. Users wishing to access corporate mail services from the Internet access via the Front End Server.
  4. The Internet access is via the following protocols: SMTP, IMAP, POP, LDAP, HTTP, XMPP, CalDAV

Traffic on the connections to the Front End Server

Traffic on the Internet connection to the Front End Server

Traffic Cause
SMTP Outgoing mail
HTTP Users connecting to their mail boxes from the Internet, using the web mail client. This traffic will be forwarded to the Mail server.
LDAP Users accessing their address books or authenticating against the directories hosted on the corporate setup from a desktop client.
POP/IMAP Users connecting to their mail boxes using a POP/IMAP client from the Internet will generate POP/IMAP traffic. This traffic will be forwarded to the Mail server
XMPP Users using the chat/IM facility via XMPP from their desktop and mobile chat clients. This traffic will be forwarded to the Mail server
CalDAV Users using the Calendar facility via CalDAV from their desktop and mobile calendar clients. This traffic will be forwarded to the Mail server

Traffic on the link between the Front end Server and the Hub/Corporate server

Traffic Cause
SMTP Outgoing mail
HTTP None
LDAP None
POP/IMAP None
XMPP None
CalDAV None

Traffic on the link between the Front end Server and the Mail server

Traffic Cause
SMTP None
HTTP The traffic which is passed on from the Front End server
LDAP None
POP/IMAP The traffic which is passed on from the Front End server
XMPP The traffic which is passed on from the Front End server
CalDAV The traffic which is passed on from the Front End server

Hub Server

Characteristics of a Hub

  1. The Hub server is required in case of a distributed setup or in case MCS is setup as an extension to a proprietary messaging solution.
  2. The Hub server is in the trusted zone of an organization and is accessible to all the mail servers in the distributed setup.
  3. The job of the Hub server is to route mail to the destination mail server.
  4. User addition / deletion is also done on the Hub server and automatically replicated to the other servers in the network.
  5. The extension to proprietary email setups is done at the hub server.
  6. The Hub server is also the server on which the mailboxes for roaming users are hosted.

Traffic on the connections to the Hub Server

Traffic on the link between Relay Server and Hub server

Traffic Cause
SMTP
  1. Legitimate incoming mail
  2. Outgoing mail

Traffic on the link between Branch server and Hub server

Traffic Cause
SMTP Incoming mail from the Internet to be delivered to branches. Mail from one branch to another routed via the hub. Outgoing mail from branches to the Internet.
HTTP None
LDAP None
POP None
IMAP Roaming users connecting via the Internet to the mailboxes hosted on their branch server, using the web mail client on the hub.

Branch or Corporate Mail Server

Characteristics of a Corporate Mail Server

  1. The corporate server is located in the trusted zone of an organization.
  2. A corporate server will host all the mailboxes of the corporate domain.
  3. Users connect to the corporate mail server via the LAN / WAN directly.
  4. Internet connections to the mail server are re-directed via the relay server.

Characteristics of a Branch Server

  1. Branch servers host mailboxes for users at a particular branch or region.
  2. These are accessed by end users either over the WAN, LAN or the dial-up connections to these servers
  3. The branch server talks to the central hub server for routing mail to the Internet or other branches.

Traffic on the connections to the Corporate / Branch Server

Traffic on the link between the Relay Server and Corporate mail server

Traffic Cause
SMTP
  1. Legitimate incoming mail
  2. Outgoing mail

Traffic on the link between Branch server and Hub server

Traffic Cause
SMTP Incoming mail from the Internet to be delivered to branches.Mail from one branch to another routed via the hub. Outgoing mail from branches to the Internet.
HTTP None
LDAP None
POP None
IMAP Roaming users connecting via the Internet to the mailboxes hosted on their branch server, using the web mail client on the hub.

Traffic on the WAN

Traffic Cause
SMTP End users accessing their mail boxes from another branch via the WAN
HTTP End users accessing their mail boxes using the web mail client from another branch via the WAN
LDAP End users accessing their mail boxes from another branch via the WAN
POP/IMAP End users accessing their mail boxes using a desktop mail client from another branch via the WAN

Traffic on the LAN

Traffic Cause
SMTP End users accessing their mail boxes over LAN
HTTP End users accessing their mail boxes via the web mail client over the LAN
LDAP End users accessing their mail boxes over LAN
POP/IMAP POP/End users accessing their mail boxes via the desktop mail client over the LAN

Traffic on the wireless broadband connections

Traffic Cause
SMTP End users accessing their mail boxes over the dial-up connection
HTTP End users accessing their mail boxes via the web mail client over the dial-up connection
LDAP End users accessing their mail boxes over dial-up connection
POP/IMAP End users accessing their mail boxes via the desktop mail client over the dial-up connection

Additional Traffic

The other processes, which generate traffic on the connections between servers, are:

  1. Mail Store Synchronization for Disaster Recovery: For example if the branch servers replicate certain mail stores to the hub server for disaster recovery, then the traffic on the connection between the branch and the hub server will depend on the number of mail stores to be synchronized, mail store size to be synchronized and the daily mail traffic.
  2. Directory Replication Across Servers: In case of a setup in which more than one MCS servers are used to set up the messaging infrastructure, then the information in all servers is synchronized by replicating the LDAP directory. The traffic generated by this will depend on the modifications made to the corporate directory at the different servers. For example if on a particular day, a large number of users is added to the central hub server, then this will generate significant traffic on all the connections to all the branch servers.
  3. Instant Messaging: If the instant messaging service is enabled on the central servers, then the networks to the server from the branches will also carry the messaging traffic.

Calculating the Daily Traffic on any link

  • SMTP Traffic = Average number of users * Average number of mails per user (incoming + outgoing) * Average mail size
  • HTTP Traffic = Average number of users logging in per day using the web client * Average page size * Average number of pages visited.
  • For the Mithi web mail client, the average page size is 100K and the average number of pages visited is 30.
  • POP traffic = Average number of users logging in per day using the desktop client with POP access * Average number of incoming mails * Average mail size.
  • IMAP traffic = Average number of users logging in per day using the desktop client with IMAP access * Average mail store size. (This will reduce if the IMAP client supports caching)
  • LDAP traffic = Average number of users logging in per day * average no of queries per user + replication load depending on the changes done on master.

Calculating the Peak Traffic

Assuming that 2/3rd of the corporate users access their mailboxes during the peak hours, this traffic is generated within 4 hours of a day.