Web-Based SMTP Server Monitoring?Round-robin and socket connection method explained.
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Lew Newlin January 26, 2007
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Web-based monitoring of SMTP email servers is normally conducted
using one of two different approaches. The first uses a socket level
connection to verify whether or not the target server is operational.
The second more comprehensive method involves sending round-robin
messages to your email system and its subcomponents. Depending on your
needs, hardware, and company size both have validity and a rightful
place. To determine what is best for your company, let’s examine both
in more detail and the advantages and disadvantages of each.
Socket
connection is the most prevalent method used by web-based monitoring
companies due to its simplicity. A DNS check is normally conducted,
then a socket level connection to port 25 of your email server is
attempted. If DNS is ok and SMTP port 25 handshaking occurs, the
server is viewed as operational. If not, the appropriate notification
methods are triggered. The socket connection method advantages are:
speed, low bandwidth, and no agent or server changes are required.
Because of its simplistic design, socket connection monitoring can be
used to monitor SMTP servers your company does not own or manage. The
disadvantage to this approach is accuracy. Just because DNS is
operational and handshaking occurs, it does not mean the server or
subcomponents are actually processing messages.
The second,
less used, method involves a round-robin process that actually sends
test messages to your email systems and waits for the message to be
returned. As with the socket connection method, a DNS check is normally
performed first. A test message is then sent by the monitoring company
to your email system. The message travels through your gateways, any
subcomponents such as antivirus and content/spam filters, through the
firewall to the designated internal server. The internal server, based
on a pre-established server-based rule, returns the message back to the
monitoring company. If the message is received by the monitoring
company within the preset time, 15 or 30 minutes for example, the email
system and subcomponents are viewed as operational. If not, the
appropriate notification methods are triggered.
If
you are using Microsoft Outlook & Exchange, a server-based rule
would look something like this: Apply this rule after the message
arrives from [email protected] and with "Email Verification for" in the subject forward it to "[email protected]
The
advantage of this approach includes the ability to check the complete
message process for failures. For example, a gateway checked using the
socket connection method could be fully operational, yet a connected
spam filtering appliance or antivirus process could be hung halting
message processing. Depending on the monitoring company, the ability
to include a specific type of attachment to the round-robin process is
also available. Including an attachment such as the Eicar.Txt text
pattern for example, permits subcomponents such as antivirus to be
fully tested. The disadvantages to this approach are: increased
processing by your servers as this testing method sends 96 messages per
day using a 15 minute monitoring interval; creation of an email account
to receive the test message; and establishment of a server based
rule.
The diagram below outlines the process for both round-robin and socket connect monitoring methods.
Diagram of email server
round-robin and socket connection montoring methods. Clearly,
the round-robin method offers a more comprehensive testing process than
the socket connection method. However, depending upon your needs both
process have a rightful place in verifying your email systems are up
and operational.
If you do not have the ability
to establish server based rules, your only choice is to use monitoring
based on the socket connection method. If you have the ability to
establish rules, the round robin process offers a much more
comprehensive testing method.
Socket connection type
monitoring is offered by a wide range of companies and prices vary
widely. Round-robin processing is offered by SiteRecon and
Websitepulse and range from $11 to $29 per month depending on the
monitoring frequency.
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