Allow Restricting Address Resolution to IPv4 or IPv6

[bash]

[bash]

I'm not sure about the name inet_protocols: I originally got it from Postfix, but I'm not sure if it's the clearest name. What do you think?

[marlam]

I always thought that options to choose IPv4 vs IPv6 are just workarounds for broken network setups, because these things should be invisible to applications.

And for workaround purposes, source_ip / --source-ip should be sufficient, even though it requires a system-specific argument.

Is there really a use case for a general inet_protocols option?

[bash]

Agreed, it is a workaround.

My motivation for disabling IPv6 is that spam lists like the one from Spamhaus block entire /64 blocks for IPv6 addresses (source). Avoiding IPv6 in that case was easier for me than either getting my provider to give me an entire /64 block (which I doubt they would do).

And for workaround purposes, source_ip / --source-ip should be sufficient, even though it requires a system-specific argument.

I didn't know about that option, thanks :) The workaround works well enough for me, so I'm totally fine if you reject this PR.

[marlam]

OK, thanks for your understanding, I will reject this PR now.