Hello,
Many of our clients (some of them are using your business product) complain recently that Avast is blocking our mail application. Our investigation shows that Email shield combined with IPv6 network is preventing .net Socket to connect. On every client machine we see those entries in C:\ProgramData\AVAST Software\Avast\log\Mail.log
[2019-05-17 09:22:31.294] [info ] [MailShield ] [14332:12000] IMAPs Connect to IPv6 address, dropping
[2019-05-17 09:22:31.794] [info ] [MailShield ] [14332:12000] IMAPs Connect to IPv6 address, dropping
[2019-05-17 09:22:33.811] [info ] [MailShield ] [14332:12000] IMAPs Connect to IPv6 address, dropping
[2019-05-17 09:22:34.312] [info ] [MailShield ] [14332:12000] IMAPs Connect to IPv6 address, dropping
[2019-05-17 09:22:34.813] [info ] [MailShield ] [14332:12000] IMAPs Connect to IPv6 address, dropping
[2019-05-17 09:22:36.816] [info ] [MailShield ] [14332:12000] IMAPs Connect to IPv6 address, dropping
[2019-05-17 09:22:37.317] [info ] [MailShield ] [14332:12000] IMAPs Connect to IPv6 address, dropping
Our investigation shows that Avast is blocking Sockets created with option IPV6_V6ONLY == false (https://docs.microsoft.com/en-us/windows/desktop/winsock/ipproto-ipv6-socket-options ). This is the socket option that allows both for IPv4 and IPv6 communications
Here sample C# code that reproduce the issue (socket.DualMode = true is switching the socket option IPV6_V6ONLY = false)
var socket = new Socket(AddressFamily.InterNetworkV6, SocketType.Stream, ProtocolType.Tcp);
socket.DualMode = true;
// outlook.com imap server
socket.Connect("imap-mail.outlook.com", 993);
Here sample application in C# that reproduce the issue
https://drive.google.com/file/d/18MMBg3dTGZgtGanOaP5oc-x2xQkMLDp_/view?usp=sharing
Hello,
Many of our clients (some of them are using your business product) complain recently that Avast is blocking our mail application. Our investigation shows that Email shield combined with IPv6 network is preventing .net Socket to connect. On every client machine we see those entries in C:\ProgramData\AVAST Software\Avast\log\Mail.log
[2019-05-17 09:22:31.294] [info ] [MailShield ] [14332:12000] IMAPs Connect to IPv6 address, dropping
[2019-05-17 09:22:31.794] [info ] [MailShield ] [14332:12000] IMAPs Connect to IPv6 address, dropping
[2019-05-17 09:22:33.811] [info ] [MailShield ] [14332:12000] IMAPs Connect to IPv6 address, dropping
[2019-05-17 09:22:34.312] [info ] [MailShield ] [14332:12000] IMAPs Connect to IPv6 address, dropping
[2019-05-17 09:22:34.813] [info ] [MailShield ] [14332:12000] IMAPs Connect to IPv6 address, dropping
[2019-05-17 09:22:36.816] [info ] [MailShield ] [14332:12000] IMAPs Connect to IPv6 address, dropping
[2019-05-17 09:22:37.317] [info ] [MailShield ] [14332:12000] IMAPs Connect to IPv6 address, dropping
Our investigation shows that Avast is blocking Sockets created with option IPV6_V6ONLY == false (https://docs.microsoft.com/en-us/windows/desktop/winsock/ipproto-ipv6-socket-options ). This is the socket option that allows both for IPv4 and IPv6 communications
Here sample C# code that reproduce the issue (socket.DualMode = true is switching the socket option IPV6_V6ONLY = false)
var socket = new Socket(AddressFamily.InterNetworkV6, SocketType.Stream, ProtocolType.Tcp);
socket.DualMode = true;
// outlook.com imap server
socket.Connect("imap-mail.outlook.com", 993);
Here sample application in C# that reproduce the issue
https://drive.google.com/file/d/18MMBg3dTGZgtGanOaP5oc-x2xQkMLDp_/view?usp=sharing
What happens if you disable IPv6 and only use IPv4?
We may need for you to submit a case at https://www.avast.com/business-support-contact
I can’t test that now. However I tested if IPv4 sockets work and they work fine. IPv4 over IPv6 (https://tools.ietf.org/html/rfc7040 ) is not working