I’m using the latest version of Avast Free Antivirus (build 17.9.3761.0) on Windows 10. Thunderbird stopped sending email about a week ago with the following message:
“An error occurred while sending mail: The mail server sent an incorrect greeting: Cannot connect to SMTP server 2604:4f00::1:0:0:182 (2604:4f00::1:0:0:182:587), connect error 10061.”
It also wouldn’t receive email but there was no visible error message for that.
The problem was circumvented by disabling Avast Mail Shield.
I was told that the mail server in the above error was using an IPv6 address. So I tested IPv6 connectivity on my network and found that it was broken.
I disabled IPv6 on my network (Network and Sharing Centre > Connections: connection name > Properties), enabled Avast Mail Shield, and the problem has disappeared.
So I have two questions:
- Is the email really being checked by Mail Shield now, or has disabling IPv6 on the network had the same effect as bypassing Mail Shield?
- Why doesn’t Mail Shield fall back to an IPv4 connection when the IPv6 connection isn’t working?
Program versions:
Avast: version 17.9.2322 build 17.9.3761.0
Windows 10 Home: version 1709 build 16299.125
Thunderbird: version 52.5.0 (32-bit)
Thanks,
Ian