On Wed, Oct 26, 2022 at 11:15:25AM +0100, Matt Caswell wrote: > > I'm not promising anything. But if you send me the captures I can take a > > look at them. > > I've taken a look at the captures for the working and non-working scenarios. > > Do I understand correctly that your application is acting as the server > in this setup? > > I have compared the working and non-working captures. In both cases the > ClientHello is successfully received, and the server responds with a > ServerHello, Certificate, ServerKeyExchange and ServerHelloDone message. > Aside from normal variations between one session and another, AFAICT, > the ClientHello and the server's response messages all look identical > other than the server obviously has a different Certificate. The > Certificates themselves also look identical to each other other than the > subject/subjectaltname being for a different server. The intermediate > certs are the same in both cases. > > Following the server's ServerHelloDone the client continues with a > ClientKeyExchange message in the working case. In the non-working case > the the client immediately closes the TCP connection without sending any > kind of alert. See longish thread at: https://marc.info/?l=postfix-users&m=166584042429636&w=2 which describes a remarkably similar set of symptoms observed after a Microsoft patch update. Today the OP posted that a more follow-on patch appears to have resolved the problem. > This really looks like a problem on the client side to me. Yes, the client just hangs up. A known. Disabling session tickets on server appears to help in some cases (for no obvious reason). Applying the follow-on update is a better solution if applicable. -- Viktor.