Hi, all,
I've been having the exact same problem with Outlook 2016...two iexplore.exe processes are launched whenever I open Outlook, and then my computer performance tanks and basically becomes inoperable.
When looking at the Task Manager details tab, I noticed two things about the iexplore.exe processes that struck me as unusual...first, one of the two processes was only using about 60K of memory, while the other was using several megabytes. That wasn't too
weird at first, but that same process was frequently changing status from "Running" to "Suspended" and back again.
If I ended these processes, they would just start right back up again.
I tried disabling all add-ins in Outlook, running in safe mode, but nothing worked.
I saw a tip in another forum (https://social.technet.microsoft.com/Forums/office/en-US/de34e4b2-0c48-4486-ab75-0a54136748d1/outlook-2016-crashing-internet-explorer?forum=Office2016setupdeploy)
suggesting a clean windows reboot might help.
I was a bit nervous about doing the full clean reboot, so I decided to try a modified approach...I opened the System Configuration utility ([Windows]+[R] and type "msconfig") and changed the "Startup selection" on the General tab to "Diagnostic startup."

I then rebooted the computer and logged back in. I opened Outlook, but forgot to check whether the iexplore.exe processes were still running. Then I changed the System Configuration startup selection back to "Selective startup" and checked the "Load system
services" and "Load startup items" checkboxes and rebooted again.

After this, I rebooted the computer and logged back in. Since doing this, whenever I open Outlook 2016, I get 4 (instead of 2) iexplore.exe processes running, but my computer runs just fine. I also noticed that all 4 iexplore.exe processes are using several
MB of system memory, and none of them are toggling between "Running" and "Suspended" status. It's only been about 30 minutes so far, but it seems for now that this reboot process resolved the issue, and I am able to work productively again.
I hope this helps someone else who might be experiencing this problem.