Based on the details provided so far, I think you should turn the foozle-knob until the whatsit level drops. :-)
> On Jun 25, 2019, at 11:09 PM, Warren Toomey <w...@tuhs.org> wrote: > > One of my list members has his own SMTP server. He's configured it to return > a large multiline response to the initial EHLO from a client. Apparently > when my Postfix installation connects to him, it sits idly after the multiline > response and never goes on to issue further SMTP commands. > > Is there a configuration setting that I've overlooked to allow the Postfix > client to deal with this situation? I'm running version 3.3.0 on Ubuntu > server. Or you could be more specific, and post the full EHLO response from that server, even better would be the same, plus the server hostname. -- Viktor.