When users migrated from MS Exchange to Google Apps Gmail there were numerous problems where shared access with the same mailbox occurred. This is a simultaneous connection error. This is used for when users need to set up the account on a number of different Macs so that each user could respond to customer support queries from a central mailbox.
The error that started to appear for users was too many simultaneous connections this message was sent from the Gmail server. Google implemented only 10 connections to any imap mailbox, which cause this problem. As part of the migration from exchange, we also took the opportunity to migrate away from MS Outlook and install the Mozilla Thunderbird, which includes the lightning plugin for the calendar functionality. Parts of the Thunderbird settings allow you to specify the number of cached IMAP connections to use on a mailbox, the default being five. Changing this to one forced all users to stick to a single connection to the shared mailbox.
To do this you right click account, then select account settings and advanced. Then select IMAP and you will be at the option of the maximum number of server connections to cache setting. This should limit each user allowing up to ten different users to connect to the same IMAP mailbox.
If you find you are still having trouble with this issue our technicians are located in Brisbane and travel to you. They help with Apple support and service for personal or business.