When mail notification (through mailer-plugin) is active in the post build action of the job, if we launch 2 job in paralel (option "Execute concurrent builds" active), the first job wait the end of the other to finish.

If we disable mail notification (mailer-plugin), or if job time execution is not so long (i don't know exactly how many time) everything is ok.

It seems there is a lock between concurrent builds using mailer-plugin.