How much mail can I send through my server?

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Question

I want to work out how much mail I can send through my mail server – how do I do this?

Answer

This question is a bit like asking "How long is a piece of string?". There are a huge number of factors which will affect how much mail your server can process, which makes it very difficult to give an accurate answer.

Firstly, if you are running GMS Communication Server, your license will include a maximum number of postings that can be achieved per hour – you cannot exceed this for posts generated by GLCommunicator. Throughput of normal mail is not affected.

If you are running a GMS Enterprise license, or a Firewall license, there are some calculations you can perform to get an approximate idea, and further calculations you can do to make this more accurate.

When trying to determine how much mail you can process, factors that you need to consider are:

  • Bandwidth
  • Size of Messages
  • Expected number of failures

The calculation you perform is:

Total amount of data to send
---------------------------- = number of seconds to send all data.
    Bandwidth per second

Say, for example, that you wanted to send 500,000 messages through your server:

Assuming that you have a 2Mb connection to the internet, and that the message you are sending out is 10KB in size, you can calculate how long this will take, if the connection runs at it’s maximum speed.

2 Mbps= 256KiloBytes/second = 0.25MegaBytes/second
10KB x 500,000 messages = 5000000KB of Data
5000000KB = 4882.8MB of data, or 4.76GB of data.
4882.8/0.25 = 19531.2 seconds required to send data.
19531.2 seconds = 325.52 Minutes
-----------------------------------------
5.42 hours required to send all messages.
-----------------------------------------

This assumes however that the entire 2Mb internet connection is devoted at
all times to sending mail and nothing else. This is actually very unlikely
to happen, and we can assume that at the very least some of the connection
is used for the protocol transmissions, and for DNS queries etc. This will
increase the figure slightly, but not by a huge amount. Also it is safe to
assume that of the 500,000 messages, a number will fail to be delivered, or
will be returned by other servers. If we assume a failure rate of 5
percent of the messages, then we can say that approximately a further 244
MegaBytes of data will be returned to your server. This will then mean
that delivery will be slowed further. Assuming that there is other traffic
on the line also, this demonstrates how difficult it is to calculate how
much mail you can send.

Note that GMS Communication Server uses compression technology and this may have a
dramatic affect on the time required. In the best case, the quantity of
data can be reduced to 1% of the figures above. This would mean that
GMS Communication Server could deliver 500,000 messages in just 40 minutes.

Further factors that can impact mail server performance are:

  • Available free disk space
  • Disk I/0 performance
  • Disk fragmentation levels.
  • Other network traffic
  • Retry times
  • DNS response times
  • external connection availability (some firewalls limit the number of
    simultaneous outbound connections)

  • Error modes of external mail servers
  • Availability of destination servers

Any of these or other factors mean that any estimated figure that you work out using the above calculations are only approximate, and it should not be assumed that this performance will be achieved.

Note: For smaller licenses such as 25, 50, 100 and 250 accounts the performance of the incoming SMTP service is restricted to a level appropriate to the number of users on the server. Consequently for those licenses incoming SMTP will not be able to accept messages as quickly as the POST service can deliver them onwards.

See Also:

Keywords:number of messages, how much, many, mail, throughput

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