EWS Autodiscover takes 16+ Seconds to Discover Mailbox server for O365 user

Exchanger Hybrid setup with an On Premise Exchange 2010 server.

We have some backend Managed EWS code that accesses user mailboxes and we are using the AutoDiscover to return the Mailbox server URL for the user.   The code before would take less than a second to return the on-Premise server URL, though now when we query for a O365 user it takes 16 or so seconds to return the Mailbox server URL.

Is this always going to be the case when querying for a O365 user?

RedirectionCallback: https://autodiscover-s.outlook.com/autodiscover/autodiscover.xml

Query: <O365User>@costono.com

Query: <On-PremUser>@costono.com

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Scott TownsendIT DirectorAsked:
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Jose Gabriel Ortega CastroCEO Faru Bonon IT - EE Solution ExpertCommented:
Well it's pretty much the time it takes.
At least you give the full "EWS" address.

The flow is as follows
HTTP (within a server)
Http redirection (to O365)
SRV DNS record

If it's taking too much time makes sure your autodiscover is set to your On-premises since it's the one that can do the redirection, O365 doesn't do any redirection to your on-premises.

Also you can test the autodiscover service using ECA

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