What does ""Only one usage of each socket address (protocol/network address/port) is normally permitted" mean?
This error means all available ports on the machine are being exhausted.
By default the OS only has around 4000 ports available that are not reserved by the system. When any network connection is closed, it goes into a TIME_WAIT state for 240 seconds and cannot be reused until this wait state is over.
For example, if there are 16 connections per second for 4 minutes (16*4*60=3840), you will exhaust all the ports shortly thereafter. If HAS and the MTA are on the same machine, this exhaustion will occur sooner. This is because in addition to them communicating with one another and taking up two ports, the MTA uses a significant number of ports to send mail.
How do I resolve this error?
You can fix this by modifying the below values.
Increase the dynamic port range. The max by default is 5000. You can set this up to 65534. HKLMSystemCurrentControlSetServicesTcpipParametersMaxUserPort is the
key to use.
Reduce the TIME_WAIT state. The default setting is 4 minutes, but you can set this to 30 seconds. HKLMSystemCurrentControlSetServicesTcpipParametersTCPTimedWaitDelay is the key to use.
After these changes are made, the system must be restarted.
For more information, please refer to this Microsoft article.