How to Fix Exchange Server “421 4.3.2 Service not available”

When I examined the receive connector logs to identify the problem with the mail traffic I was experiencing on one of my Exchange servers, I saw that the error “421 4.3.2 Service not available” was constantly repeated.

When I followed the mail flow in the log, I observed that the steps continued successfully, but at the last stage it gave the error “421 4.3.2 Service not available“.

auth login,
334 authentication response,
SMTPSubmit SMTAccept,
235 2.7.0 Authentication Successful,
Mail From : <…@…>,
421 4.3.2 Service not available,

I checked the ServerComponentState of the server, and saw that the HubTransport was Draining.

Get-ServerComponentState (hostname)

To fix this situation, we need to use the following command.

Set-ServerComponentState ExchServerName -Component HubTransport -State Active -Requester Maintenance

Check again Get-ServerComponentState (hostname)

Have a nice day !

2022 H1 Cumulative Updates for Exchange Server

In the previous post, I shared that Microsoft has changed the update service for exchange servers.

It has been announced that the updates will now be released as H1 and H2, at which point the updates for the first 2021 H1 have been released.

It is reported that the new released cumulative updates(CUs) include previous security updates(SUs) and fixes for customer reported.

These updates are available for the following specific builds of Exchange Server:

Exchange Server 2019 CU12
Exchange Server 2016 CU23 (The latest cumulative update package of Exchange 2016 won’t be H2 ! )

Please check knowledge base articles for known issues via CU12 or CU23

Further Information and Guidance
Exchange Team Blog
Upgrade Exchange to the latest Cumulative Update
Exchange Updates Step-by-Step Guide
How to Find Exchange Version and Build Number

Have a nice day !

Exchange Server Update Servicing Model Changed !

Microsoft announced in the bulletin it shared yesterday that it has changed the update model for the Exchange Server.

Updates published quarterly (March, June, September, and December) were changed after feedback from customers. And they announced that they have commissioned a new update service.

In the announcement, two CU’s per year – will releasing in H1 and H2 of each calendar year, with general target release dates of March and September (these dates may change).

Next CU will be released in H2 of 2022 only for Exchange 2019, has ended CU’s for Exchange Server 2013 and Exchange Server 2016, only SUs will be released.

Have a nice day !