According to the Gmail Terms of Use,
each user account is intended for single use. This means that if you
have multiple users frequently accessing the same account or more than
one IMAP client accessing Gmail at the same time, you may reach a
connection threshold and receive the error message, 'Too many
simultaneous connections.'
Gmail currently has a limit of 10 simultaneous IMAP connections per account.
Please note that your mail client may actually open multiple
connections in the background. This means it's possible to reach a
connection threshold simply by using only two mail clients to access
the same account at the same time.
If you often use multiple mail clients or mobile devices with the
same Gmail account, we recommend closing and/or signing out of any mail
clients you're not actively using.
