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I'm researching whether Javamail is threadsafe, in particular in a situation with many sessions corresponding to different users, several SMTP servers and the use of creating MIME messages and use of transport.sendMessage method. I know Javamail is oriented toward desktop-use which makes me suspect it may not have been built with threading in mind, and am wondering if anyone has such experience.
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Yes it is thread safe once constructed.
The App Engine Mail API (which also supports JavaMail) has already been deprecated. Instead, GCP recommends to use a third-party mail provider such as: SendGrid.
SMTPTransport t = (SMTPTransport)session. getTransport("smtps"); t. send(message); String response = t. getLastServerResponse(); boolean s = t.
The JavaMail API provides a platform-independent and protocol-independent framework to build mail and messaging applications. The JavaMail API is available as an optional package for use with the Java SE platform and is also included in the Java EE platform.
Admittedly the thread safety rules for JavaMail are not well documented, but hopefully they mostly match what you would expect.
Multiple threads can use a Session.
Since a Transport represents a connection to a mail server, and only a single thread can use the connection at a time, a Transport will synchronize access from multiple threads to maintain thread safety, but you'll really only want to use it from a single thread.
Similarly, a Store can be used by multiple threads, but access to the underlying connection will be synchronized and single threaded.
A Message should only be modified by a single thread at a time, but multiple threads should be able to read a message safely (although it's not clear why you would want to do that).
Hope that helps...
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