Not sure how relevant these are but anyway...
When modifying SMTPSender to send messages to all users on one domain in one go, I noticed that transport.send() throws a SendFailedException if sending to any of the addresses fails, and does not actually send to any of the addresses. The SendFailedException lists the valid sent addresses (always empty in my tests), the invalid unsent addresses and the valid unsent addresses. I built in some looping precisely with mailing lists/nukes in mind to retry the valid unsent ones, since we don't want all 100 receivers to fail when only one of them is invalid. This was done for head though, and the internal retry count is 3 (I had originally set it to 5 so that is why this rang a bell)
Before the branch I removed the thing in SMTPSender where it avoids sending to more than one user on the same domain due to some assumption that JavaMail sends to all recipients in the To header on a given domain even if only one is specified in the to parameter for the transport.send() method. This was tested pretty thoroughly by myself and you http://www.jboss.org/index.html?module=bb&op=viewtopic&p=3830218#3830218, so I don't know if that could be it either. I certainly could not reproduce this behaviour, and before this fix I was getting too few mails sent out, i.e. if kab@bigfoot and kab2@bigfoot only kab or kab2 would receive the mail. Having said that whoever added this must have done so for a reason, or maybe used (knowledge of) a previous version of JavaMail or something?
yeah I used to get dupes and so I put that in....hummm
But I don't thinks thats it, because I kept sending it LONG after it was to all receipients. Basically it sent the message until I shut down. I'll try the M1 branch with your fixes this weekend and see if I can figure it out.