Hello, I posted something similar to this on the MacOS X newsgroup, and I thougth I would post here as well.
On MacOS X, I will get at least four or five hangs per day, exactly like this: I compose a message, then I hit send. Then the "sending mail progress" dialog comes up. It first says "Sending mail". As soon as it switches to "Delivering mail", it hangs with the spinning cursor. It does not happen every time, but it happens far too often. I know the mail server that I am connecting to runs Sendmail 8.11.3. I also use Mozilla on Windows 2000, and I don't have this problem. I filed a bug, take a look. http://bugzilla.mozilla.org/show_bug.cgi?id=123574 Brian!
