I'm hoping someone can help me. We just upgraded our mail servers to only support tls 1.2 and to not support other security methods. We also turned off the clear text password authentication and now several customers are having trouble connecting. I've been able to get most customers on the right path but I'm stuck on a couple.
#1 a customer on a newer mac using mail there. They can only seem to connect without ssl enabled for incoming. For outgoing smtp they also cant connect securely, on the server i see the following message:
Exception negotiating TLS session: System.Security.Authentication.AuthenticationException: A call to SSPI failed, see inner exception. ---> System.ComponentModel.Win32Exception: The client and server cannot communicate, because they do not possess a common algorithm
Usually when I've seen this error its been because of Windows 7 and by getting the customer to enable the tls 1.2 support it works.
In the case of this customer their operating system is newer says it supports TLS but they are still unable to connect. Anything different we have to do to get this working on a mac? There doesnt seem to be a choice for TLS, you just say to use SSL and there is a checkbox for that, no choice to pick TLS or SSL connection.