Stress test of mailservers


We subjected 3 mailservers to a simple stress test to get a baseline comparison of their performance in a situation where they are overwhelmed with a large number of email messages to deliver.

In order to narrow down the selection of possible email server solutions, we decided to run stress tests on IceWarp, MailEnable and Kerio Connect servers. The test was fairly simple, but showed significant differences between the alternatives. We wanted to find out how the mailserver will behave in situations with excessive load, what will be its responses and how its web interface will behave after the crawl.

The test was performed on a virtual server with Windows Server 2008, which was assigned one core at 1.5 GHz and 2.5 GB of RAM. The test consisted of sending 50 000 mails of about 5kB to each mailserver, using a simple PHP script. The processing time of mails was determined by the start of sending messages from PHP and displaying the last received one in the web mail client. The conditions were the same for all mailservers.

Mail processing time:

  • IceWarp – 36 minutes
  • MailEnable – 197 minutes
  • Kerio Connect – 515 minutes

Last but not least, we also looked at the response of the web client. With a large number of messages, almost every web client had their hands full, especially when scrolling through them. The only one of the clients that worked without any major problems, despite the overload of messages, was the Kerio Connect client, as it did not use AJAX for paging. However, this fact is not so important, because the mailserver will ultimately run on a server with a much more powerful configuration, where even a larger amount of mail in the mailbox should not be a problem.

The highest score in our test was clearly IceWarp, which is more than 5x faster than MailEnable and 14x faster than Kerio Connect. While this test was neither detailed nor extremely sophisticated, it did show clear performance differences.