Problem connecting to Office 365 Outlook.com (version 2015 R4 and 2015 R4.1) - IMAP, SMTP, POP3

Question

Connecting to office365 accounts with recent version of Rebex Secure Mail causes exception.

This is the error message we get:

Rebex.Net.TlsException: Connection was closed by the remote connection end. ---> Rebex.Net.TlsException: Connection was closed by the remote connection end.
in Rebex.Net.ZHB.PD()
in Rebex.Net.QV.FB(TlsParameters A)
in Rebex.Net.Imap.XM(String A, Int32 B, TlsParameters C, SslMode D)
--- Fine della traccia dello stack dell'eccezione interna ---
in Rebex.Net.Imap.XM(String A, Int32 B, TlsParameters C, SslMode D)
in Rebex.Net.Imap.WM(String A, Int32 B, TlsParameters C, SslMode D)
in Rebex.Net.Imap.Connect(String serverName, Int32 serverPort, SslMode security)

What could be causing these problems and how can we resolve it?

Answer 1

UPDATE

The fix for the issue with Office365 servers has been released as part of Rebex Secure Mail version 2016 R1.

---

This was caused by issues in our TLS implementation. In Rebex Secure Mail 2015 R4, we enabled TLS 1.2 by default, and Microsoft recently upgraded Office365 to from Exchange 2013 to Exchange 2016, which added TLS 1.2 support. Unfortunately, it turned out our TLS 1.2 implementation was not compatible with theirs, causing issues with Exchange and Office365 when certificate with SHA-2 signature was used by the server.

The issue will be has been fixed in version 2016R1 of Rebex Secure Mail that should be released within weeks.

Alternatively, use a hotfix build it you would like to have a working TLS 1.2 support now.

Registered customer - write us to support@rebex.net to get the full version of the hotfix. Sorry for inconevenience!