Outlook lag after mailbox moved to exchange 2016

There was no noticeable issue with my first wave of users, but I am now seeing a couple of lag-related issues in outlook.

All our outlook clients are on-prem, nobody accesses outlook externally. Our mailbox environment is pretty lean--we have 80 users but the total size of the MBDB is about 45GB

All user, shared, and resource Mailboxes are on EX16. Internal DNS and firewall is pointed at EX16. Our EX10 server is still in service but the only thing it is doing at this point is hosting the Public Folders until I run the migration process for that.

Issue one, that I'm less concerned about, is Outlook takes about five more seconds to load on average for a user who just has their own mailbox or nothing else. Before moving the mailbox, it was like five seconds or so to load for an average user, after migrating the mailbox to EX16 it is more like 10-15 seconds. It can be anywhere from 30-60 seconds if the user has full access to other mailboxes or resources. When Outlook loads, the lag occurs when the splash screen shows "loading profile," prior to the outlook icon appearing in the tray and prior to loading add-ins etc.

Thing two, I notice that dealing with additional mailboxes that I have full access to, there is a lag of up to 10 seconds if I navigate to a folder under the additional mailbox if I have not been in it for an extended period. Both my mailbox and the additional mailbox are on the EX16 server. When the mailboxeswere on EX10, the browsing was always instatnaneous unless the folder had thousands of items.

Hardware-wise the new server is a lot beefier. No hardware resources are close to maxing out (it's a physical host), plenty of RAM, not seeing any IO bottleneck. My expectation is that the new server would perform as good as or better than the old server... seems to be a mystery for now. At the end of the day, the increased lag is not life shattering but I'm concerend it could point to something being misconfigured that could be a worse problem some day.... Or maybe there's just more going in EX16 vs EX10 that would cause a little more lag via Outlook.
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AmitIT ArchitectCommented:
How is the result, when you access it via OWA. Test outlook in safe mode and see, if that make any difference. Also, you can analyze it using exrca.com. Goto client tab and run Microsoft Connectivity Analyzer Tool. Review the result.
quincycreditAuthor Commented:
Access via OWA seems to be a little quicker. Navigating folders was either instantaneous or maybe like 1-2 seconds if it had lots of items in the folder. Safe mode on Outlook made no difference... Need to check back on the exrca.com, unfortunately I'm getting a 503 error when I browse to there or testconnectivity.microsoft.com
AmitIT ArchitectCommented:
Try to reconfigure profile again and test in both cache and non cache mode. Share the result.
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quincycreditAuthor Commented:
Reconfiguring profile makes no difference.  We do still have our public folders on the old Exchange server, do you think having the public folders on the old server and just the mailboxes on the new server could account for this latency?  We cannot move them for another couple weeks.
AmitIT ArchitectCommented:
If I understand correctly, outlook is taking time, when you are opening it. Are you facing lag while browsing public folders?
quincycreditAuthor Commented:
Not really when I navigate between public folders.  I do experience a noticeable lag if I try to look at another mailbox that I have access to from within my mailbox.  Also when I click send, it will usually show the spinning wheel a few seconds and then it sends the email.
AmitIT ArchitectCommented:
Do  you have any wan accelerator device, between Exchange and client end. Like riverbed. What is client OS and Outlook version.
quincycreditAuthor Commented:
No we do not have a wan accelerator device.  The clients (98% of them) are running Windows 10 Pro with Outlook 2016.  The remaining 2% are on Windows 7 Professional running outlook 2010.
AmitIT ArchitectCommented:
Here is my advise, you install wireshark or netmon tool and trace the traffic. This might help you to find out, where you have delay. You might need help from network team to track the route and provide you the data. Or if you have option to open MS case, just open Sev B case and involve Outlook team. I remember, seeing similar issue for one of my client, after troubleshooting for a week, we found that packet size is large and firewall was not allowing large packets. Finally, we updated firewall to accept large packets and everything was back to normal.
quincycreditAuthor Commented:
yes, that was an option we were entertaining. Thanks
AmitIT ArchitectCommented:
Such issues are difficult to troubleshoot, and required multiple team or vendors help.
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