POP, IMAP, SMTP session limits

Session limits

Each email account is subject to a maximum limit of POP and IMAP connections that can be opened to Qboxmail servers from the same IP address.

The set values are more than sufficient for a normal use by a user through his email client:

  • 50 simultaneous sessions for IMAP
  • 10 simultaneous sessions for POP

It may happen that this limit is reached if you configure the same email account on an excessive number of stations and simultaneously on various devices such as smartphones if these accounts are all connected to the same corporate connectivity. In this case the problem manifests itself with an incorrect username and password. You can reset the number of active connections simply by closing and re-opening your email client. If this procedure does not work, it is possible that there are other problems to be solved on the PC, for example an antivirus or a firewall that does not close the sessions correctly even after closing the email client or because they block TLS connections. Usually on the website of the antivirus manufacturer you can find directions on how to solve the problem. Here are some links related to this topic:

To be sure that the problem with the wrong username / password is the maximum number of connections reached, it is possible to analyze the email account logs using the ETLive tool located in the control panel.


To avoid this type of problem, we advise you to configure your email account on a single PC and, if configured also on Smartphone and Tablet, to access through your connection and not via Wi-Fi or ADSL. We also recommend that you assign each person a single personal email account (ex. john.doe@domain.com) and set up generic email accounts (info@, sales@, ...) such as Email Alias to individual personal email accounts.

For more information about Email Alias, read the relevant documentation.


If you use Thunderbird you can change the number of open connections for each account in their settings: Settings > Server settings > Advanced > Maximum number of connections to the server to be kept in the cache (set it to 1).

MS Outlook

If you use MS Outlook you cannot change the number of connections opened to the IMAP server. In this case we advise you to remove the subscription of the IMAP folders that you do not use frequently and to set a control frequency for new messages between 15 and 25 minutes (this does not affect the notification of the arrival of new messages that remains in real time). The error disappears immediately by closing the email client because the connections are immediately closed also on the server side.

If the error persists, contact our technical support by opening a Ticket to perform more in-depth analysis.

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