Maxing out SMTP server concurrent connections about simple-java-mail HOT 1 CLOSED

Reviewing the documentation, I realized it can be improved so that it covers your question. I've updated it, so please have a look at How connections work without batch-module.

In your case, not having the batch-module on the class-path, unless you provide your own executorService to your Mailer, there is never more than one connection active to the server at any one time. That is, unless you manually create (multiple) Mailer instances on the fly in each of your own managed threads, which is not recommended; reuse a Mailer instances across threads and configure its thread pool separately using an ExecutorService provided to the Mailer.

from simple-java-mail.