What is the "Interval between sending" menu for?

That menu indicates the time that Mailing List Studio waits during sending between one message (or group of messages) and the other. This interval is used to not overload the SMTP server you are using. An overloaded server may refuse connections until it gets rid of the accumulated traffic. This could cause many messages to fail. It is recommended to leave an interval of 0.5 seconds.

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