If you’re looking for a fix for the Too many Simultaneous Connections error, you’ve come to the right place!

After migration from MS Exchange to Google Apps Gmail, we encountered a number of problems where we had shared access to the same mailbox – e.g a shared customer support mailbox.

We’d set up the account on a number of different PCs so that staff could respond to Customer Support queries from a central mailbox.

All appeared to be fine until one day we started experiencing an error message:

Too many simultaneous connections –  message sent from the Gmail server.

A quick search found that Google implements a 10 connection limit to any imap mailbox which caused the problem. (UPDATEThis link now suggests that the limit is 15)

As part of the migration from Exchange, we also took the opportunity to migrate away from MS Outlook and install Mozilla Thunderbird (including the Lightning plugin for Calendar functionality).

Part of the Thunderbird Settings allow you to specify the number of Cached IMAP connections to use on a mailbox, the default being 5.  We changed this to 1 to force all users to stick to a single connection to the shared mailbox.


This can be quickly achieved by changing the ”Right Click Account -> Account Settings -> Server Settings -> Advanced -> IMAP -> Maximum number of server connections to cache” setting.


In theory this should limit each client to 1 connection, allowing up to 10 clients to connect to the same IMAP mailbox. Job Done! :)