External Receiving Error with Reason: 4.3.2 - Not accepting messages at this time ('421', ['4.3.2 Service not active']) []

[Mr.my0k0k0]

Dear All,

We are using Cisco C390 since last two year, but yesterday we got the error for email receiving from external without changing anything. When we analyze the case -

We can send & receive the email from Local to Local success.

We can send the email from Local to External (Outgoing) is success.

But when we receive the email from External to Local (incoming) is fail.

When trace the message, the message arrived to Cisco C390 but can not deliver to Exchange server and detail error is as below:

(DCID 10374) Message 1586119 to john@abcd.com delayed. Reason: 4.3.2 - Not accepting messages at this time ('421', ['4.3.2 Service not active']) []

Please kindly help us if you have the solution or any suggestion.

[ppreenja]

Dear Mr.my0k0k0,

For your query on the error "Reason: 4.3.2 - Not accepting messages at this time ('421', ['4.3.2 Service not active']) []" being received, please find below the details:

This error is indicative of some issue at your mail exchange server not accepting messages (service not active) and soft bouncing messages.
The ESA processed the message and then queued it for delivery to start a connection to the next-hop but is getting an error "Not accepting messages at this time".

A 4xx SMTP error code is not a permanent error. As per protocol, this is considered a transient problem, and the appliance will keep trying to deliver the email as the next attempt may be successful.
The ESA will retry the delivery to the first one as long as they are responding to the SMTP Connections and only temporary defer the mail receiving.

As long as the destination MTA is not marked as down, the ESA will follow the protocol and retries the delivery unless a permanent error (5xx) or a hard bounce is sent which would lead to the server being marked as down, and at that stage the appliance will try the next server.

Hence, to resolve the issue, I would request you to please check with your mail exchange team or change the SMTP route on your ESA to another functional exchange server.

I hope this explains and is helpful to you.

BR,
Pratham