Thanks for your bug report.

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So apparently mIRC is not looking up DNS entries correctly on a PC with IPv6 internet connectivity.

mIRC depends entirely on the Windows Winsock API to resolve addresses.

A Windows application should not be delving into IPCONFIG to perform something as basic as DNS resolution.

If /dns -6 is not working for the user, this means that the Windows API is unable to resolve the address, probably due to a network configuration issue.

Thanks for your other suggestions. Please note that IPv6 support was added years ago and its implementation and behaviour were discussed thoroughly at the time. Its behaviour has been tweaked a few times (see versions.txt) since then but is otherwise working as intended.