By default, Outlook 2010 allows up to 10 Exchange accounts to be configured in a single mail profile. If you for some reason need to add more than 10 Exchange accounts to your mail profile, you can extend this limit to up to 9999 via a registry
tweak. IMPORTANT : Back up your registry before you make any changes to it
Start > Start Search > Regedit (run as administrator) > Go to the following location.
Value name: maxnumexchange
Value type: REG_DWORD Note 1: With a single Exchange account, you can again connect to multiple mailboxes that are hosted within the same Exchange Organization. These additional mailboxes do not count towards the accounts limit. You can see your amount of configured Exchange accounts via; File-> Account Settings-> Account Settings… Note 2: While Outlook 2010 was still in BETA, the limit has been increased multiple times during BETA refreshes. You’ll find some information still referring to a default maximum of 3 and an absolute maximum of 15. Thanks and regards, Dell_Sampad_C Dell Social Media Responder