When I send an e-mail message for distribution via a Plesk Mailman list, the entire queue is blocked and most of the messages are not delivered to the mailing list subscribers. Not only that, but all other outgoing mail is blocked and/or never arrives. The only solution I've found is to use Plesk's interface (mail queue) to delete all outgoing mail in the queue. But this means losing messages. I've been running this distribution-only e-mail newsletter since 1995, and it now has around 15000 subscribers. The list is used to send out a weekly e-mail (text only) message, once a week. I suspect part of the problem may be how Mailman sends mail -- there is apparently no way to throttle outgoing mail, so many of the destinations mailers at Yahoo, Hotmail and GMail see batches of hundreds of messages coming from the same source and IP and start blocking the mail? How can I fix this? Thanks for your help and support.