[Enigmail] Enigmail hanging when importing a public key?

[Matt]

John Clizbe wrote:
> Olav Seyfarth wrote:
>> pool.sks-keyservers.net is a DNS round robin, so you end up on some server
> 
> 
> If any of these servers are down, keyserver requests can block for a
> while until there is a timeout and GPG gives up.  You can change the
> timeout value (it defaults to 2 minutes) with:

When I do OpenPGP -> Key management. Keyserver -> Refresh all public
keys. Do I update my keyring against 1 server? Or does it
(enigmail/gnupg) make a new DNS query for each key? Something in between?
Is it different if I select a bunch of keys and do Keyserver -> Refresh
selected keys?
Is this selection (on how often to query) done in enigmail, or gnupg?