After dozens of test, we can see that the problem happens only when
javamail is used from a web application.
All mails sent in batch mode (with a RUNJVA in a CLP) are handling the
mail.smtp.localhost property correctly.
When the same classes are called from a web app, no matter what we put in
it's overridden by a domain name which comes from...???
This behaviour is exactly the same with WAS on System i and with WAS test
server within WDSC on a PC.
The main problem is that the System i WAS uses a domain name which is
formed like an email address, and, of course,
it is rejected by the smtp server.
I've put a trace of System.properties() just before opening the smtp
session, and the property mail.smtp.locahost contains the sting I put
this value is just ignored for the EHLO command.
I've not a clue about where this phantom domain name comes from.