Customer is running a web application and this web application is able to send SMTP messages, for example after a new user registration or a ‘forgot my password’ option that sends out a link for resetting a password.

This application is not always able to send out messages, when it’s not able to the following error is logged on the web server:

Service not available, closing transmission channel. The server response was: 4.3.2 The maximum number of concurrent connections has exceeded a limit, closing transmission channel.

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