Customer is running a web application and this web application is able to send SMTP messages, for example after a new user registration or a ‘forgot my password’ option that sends out a link for resetting a password.
This application is not always able to send out messages, when it’s not able to the following error is logged on the web server:
Service not available, closing transmission channel. The server response was: 4.3.2 The maximum number of concurrent connections has exceeded a limit, closing transmission channel.
Continue reading Maximum number of concurrent connections has exceeded a limit
This issue was brought to my attention by Veeam, VMware recently issues a support KB article about possible data corruption when sending large amounts of data of a virtual NIC. Any data send across the network can get corrupted, including file copies, database actions etc. Naturally this can also impact Exchange server operations.
This occurs only with Windows Server 2012 running inside the VM and when the VM is using the default E1000E virtual network adapter.
Two workarounds are available:
· Disable TCP Offloading in Windows Server 2012, but this may increase CPU utilization.
· Replace the E1000E NIC with an E1000 NIC or a VMXNET3 NIC. This is probably the best solution but it is labor intensive as it means reconfiguration of all your Virtual Machines. PowerCLI may be your friend in this case.
The root cause is currently under investigation. For more information (and updated information over time) please check the VMware support KB article.