Multiple Exchange accounts limit

How many Exchange accounts can you add to a single mail profile in Outlook 2010 or Outlook 2013?

By default, Outlook 2010 and Outlook 2013 allow 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.

With an additional Registry setting, you can even extend this limit to 370000 Exchange accounts in Outlook 2013.

Additional Microsoft Exchange Server accounts cannot be added to this profile. The maximum number of accounts have been added or your Exchange Server administrator has prohibited additional accounts.
You’ll get a notification when you’ve reached the maximum amount of Exchange accounts.

Note: 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…

Increasing the limit to 9999 Exchange accounts

To increase the limit to up to 9999 Exchange accounts, the following Registry value needs to be created.

Key: HKEY_CURRENT_USER\Software\Microsoft\Exchange
Value name: maxnumexchange
Value type: REG_DWORD

Note 1: When you are using Outlook 2013, it is also recommended to set the below Registry key to prevent some crashing issues. You can then also increase the above value to up to 370000.

Note 2: While Outlook 2010 was still in BETA, the limit has been increased multiple times during BETA refreshes. You may still find some information referring to a default maximum of 3 and an absolute maximum of 15. This no longer applies.

Increasing the limit to 370000 Exchange accounts

To increase the above limit to up to 370000 Exchange accounts in Outlook 2013, you’ll need to apply Hotfix KB2889951 or a later update. In addition, you must set the following Registry value as well.

Key: HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook
Value name: UseLargeEMSInstCtxHeap
Value type: REG_DWORD
Value data: 1