relay host with ipv6 ?

[Stéphane Guedon]

Hello

When looking at the manual to smtpd.conf, on "action" and "relay" 
nothing says the relay host has to be ipv4.

Yet, when writing my conf', it definitely looks like not to be possible 
to relay to an ipv6-only host (in my case, I wanted to dedicate a 
specific ipv6 address on the relay host).

Is it possible that the relay function only sends mail to ipv4 addresses ?

Thanks for your help and comments.