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Using F5 for SSL offloading for Exchange 2007 IMAP(993) and SMTP(465). Occasionally will get cannot connect to server errors.


We are using our f5 for SSL offloading for our mail.


Ex. Internet IMAP port 993 SSL <> F5 Load balancer <> Exchange port 143


Multiple times a day users will complain that they get errors in outlook saying outlook could not connect to exchange server. They will try clicking the send/receive button again and it will connect fine. I'm pretty sure the problem lies either in the firewall or F5 with maybe a TCP timeout but I'm not sure how I can figure this out. I used the F5's exchange 2010 wizard to set up the virtual servers for my exchange 2007 box.


  • Internet <-> Firewall <-> F5 1600 LTM <-> Exchange server
  • F5: 1600 LTM. 10.2.4 Build 591.0 Hotfix HF2
  • Email: Microsoft Exchange server 2007

Any ideas on how to diagnose this and how to potentially fix?




I'd take the most obvious, easiest step and apply HF7, the most recent HF release, first.



We had a similar issue but for internal Outlook clients over RPC. It was a TCP configuration setting that fixed it for us. We created a new TCP profile and applied to both Client and Server Protocol Profiles. The changes from default iApp in new TCP profile was Keep alive set to 120 seconds, Slow start enabled, Nagles Algorithm unchecked, and Ack on Push enabled. The iApp version we are currently on is f5.microsoft_exchange_2010_cas.2012_06_08.


Hope this helps.