Timezone for postfix - where to set it?

I've got postfix-sasl installed (via pkg) & working fine except the time stamp (I can see it for the queued emails) is apparently wrong, despite system time being OK (correct time & timezone).

Where do I need to copy the localtime file to set the timezone for postfix?

No; I don't use tzsetup. I copy the appropriate file from /usr/share/zoneinfo to /etc/localtime.

..and now I want to copy the same file to somewhere in the postfix installation hierarchy..