Sometimes when tSendMail is executed for a third or fourth time, it fails with the following message:
"Exception in component tSendMail_1
javax.mail.MessagingException: Could not connect to SMTP host: smtp.gmail.com, port: 25;
nested exception is:
java.net.ConnectException: Connection timed out"
Then tSendMail would work again after few minutes.
The server where the Job is running is an instance of Amazon AWS, which has some SMTP Sending Limits:
Fill in a form (as suggested by Amazon) to request that the SMTP limit be increased or disabled.