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Anthony K O365Flag for United States of America

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Routing SMTP Traffic

We have a secure Email Gateway appliance (SEG1 at Site 1) that is currently (temporarily)  being used to route smtp traffic from various Hosts or Domains to a Hardware Load Balancer (HLB) which then forwards to our Exchange Edge Servers at Site 2. (where another Email Gateway appliance is being used, SEG2)  We need to decommission SEG1 but there are no Email Servers at this site (No Send Connectors) . What other method can I use to bypass SEG1 at site 1 and have those Hosts or Domains send to directly to the HLB?
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David Favor
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You asked, "What other method"...

Remove all the complexity above.

The SMTP protocol already implements fault tolerance + load balancing as part of the protocol.

Replace all the above with multiple MX records at the same priority for all your Exchange Edge Servers, to achieve load balancing.
MX Records may help (as David said) as long as your Hosts are using them. A lot of services may use a dedicated server name for the mail transport.
The best option is always to use a DNS Alias Name for mailservers, as it is easy to change, just by changing the DNS record.
If SEG1 should be taken out of order, and there ar servers pointing to this device, you can switch it off and add an alias name with the SEG1 name to point to the IP of your HLB. This way SEG1 is an alias fro HLB.

if a direct connection to the IP of the HB is not possible, you don't need an email server.
In fact, you can still install (and configure) the SMTP service on a Windows server (Even 2016 ou 2019) from the Features. Note, that some parts of IIS are installed for the management of this service.

It could also be possible to use an equivalent service on a Linux.
You will be able to stop and disable this service when SEG1 come back.
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You stated  "if a direct connection to the IP of the HB is not possible you don't need an email server"...suppose it is possible via a host file? Would an email server be necessary? Please clarify.

Avatar of DEMAN-BARCELO (MVP) Thierry
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Thanks much Deman! I'll give these ideas some traction as well as Bembi Alias comments. 
thanks much!!