Exchange 2016 POP3 configuration

I have a Client that uses Reynolds & Reynolds to send and receive emails to/from customers with the program. They are able to send but not receive. Spoke with R&R support and they use POP3/port 995 to receive emails to the program. I'm trying to configure POP3 and think I have everything set but I'd rather be 120% sure rather than leave a security risk open.

In Management Shell I ran the >Set-PopSettings to configure everything and when i run Get-PopSettings I get

InternalConnectionSettings : {Exchange.Domain.local:995:SSL, Exchange.Domain.local:110:TLS}
ExternalConnectionSettings: {email.domain.com:110:TLS, email.domain.com:995:SSL}
UnencryptedOrTLSBindings: {x.x.x.x:110} (x.x.x.x = external exchange IP)
SSLBindings:                             {x.x.x.x:995} (x.x.x.x = external exchange IP)
Cert Name                                 email.domain.com

Does this look correct? Should the Binding be the External IP or Internal? Testing using Microsoft Analyzer (https://go.microsoft.com/fwlink/p/?LinkID=313839) fails with

Test TCP port 995 on host email.domain.com to ensure its listening and open. The specified port is either blocked, not listening, or not producing the expected response.

Any help is appreciated and if you need more info let me know.

Thank you!
LVL 1
bensonwalkerAsked:
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timgreen7077Exchange EngineerCommented:
Make sure that pop is enabled on all your exchange servers, and make sure the firewall isn't blocking those ports and forwards traffic on those ports to your exchange servers. Your settings look fine check firewall.
Sebastian TalmonSystem Engineer Datacenter SolutionsCommented:
Are the pop3 frontend- and backend services running?

In a default Exchange Installation the pop3 services are configured as manual start, not automatic. You should reconfigure them as automatic and start the services, if you want to use pop3
bensonwalkerAuthor Commented:
I will check Firewall but i think Sebastian may be onto something. Both Services are set to automatic but only POP3 Backend is running. When i try to start POP3 i get

"The Microsoft Exchange POP3 service on Local Computer started and then stopped. Some services stop automatically if they are not in use by other services or programs."

Quick google search suggested checking receive connector bindings but nothing came back on 995 or 110 ... i did notice that the bindings that were returned to me all looked like {[::]:587, 0.0.0.0:587} and when i look at the bindings for POP3 i have

UnencryptedOrTLSBindings: {1.2.3.4:110}
SSLBindings:                             {1.2.3.4:995}

where 1.2.3.4 = my external IP. Should this not be configured? Should it instead return back {0.0.0.0:995}  ?
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Sebastian TalmonSystem Engineer Datacenter SolutionsCommented:
is the external IP directly on one of the network interfaces? Or only through NAT or proxy routed to the Exchange Server?

If there is no need to restrict pop3 access, I would set it back to 0.0.0.0
bensonwalkerAuthor Commented:
It's set through a sonicwall nat policy. I would use the same Set-PopSettings [-SSLBindings 0.0.0.0:995] correct?

This won't open us up to anything undesirable will it? Spoofing/hacking, etc? That is my main concern
timgreen7077Exchange EngineerCommented:
No it will not. You will still need to authenticate so you should be fine.
Sebastian TalmonSystem Engineer Datacenter SolutionsCommented:
I think that is the reason why the service is not starting - it can not bind to an IP that is not registered on the host itself.

Binding of a protocol / port to one IP has nothing to do with authentification / security. It is only relevant if your Exchange Server has multiple IP Addresses, and you want to limit this protocol to one of the IP Adresses.

https://docs.microsoft.com/en-us/exchange/clients/pop3-and-imap4/configure-pop3?view=exchserver-2016

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bensonwalkerAuthor Commented:
Set the bindings back to 0.0.0.0 and both services started/are running. Thank you everyone!
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