I have an exchange 2013 server fronted by anti-spam unix servers. Once in a while i get this:

status=deferred (delivery
temporarily suspended: host xxxxxxx refused to talk to me: 421 4.3.2 Service not available)

I have to restart the transport service on exchange and mail start flowing again. Is it related to the amount of connections?

Thanks

Hello,

I recommend you use test-servicehealth cmdlet to check if all required exchange services are started.

If these services are started, I recommend you disable AV to check the result.

Here is the similar thread for your reference.

http://social.technet.microsoft.com/Forums/exchange/en-US/606e823b-74ee-486c-b074-9d88c69904f5/421-432-service-not-available

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