The Symantec Messaging Gateway(SMG) server is installed on guest OS on ESXi host, the memory and CPU configuration is considerably sufficient. However the SMG might still experience slowness when deliver messages.
16GB RAM, 4 CPUs, E1000 was used as network adapter in SMG.
E1000 was used as network adapter in SMG, although it is supported by SMG, however it is an old adapter type and transmission speed is not as good generally speaking.
Please note if there is a need to switch to a different network adapter model, this is currently supported for new installations only.
Below steps are not officially supported.
power off gust OS.
remove E1000 adapter and add new adapter with vmnet3.
open SMG host and following the KB to configuration NIC teaming in ESXI