Send it by airmail.
An airmail stamp.
Send the letter airmail.
A terrific bargain at the current price of $ 26 including airmail postage overseas.
Turn your covers into cash, or cash equivalents, by selling to Airmail Collector.
Dates for registration will be considered to be met assuming that legible postmarks are on or before the dates and airmail is used.
The two 1d Australian stamps are not postmarked, presumably because the New Zealand airmail stamp more than paid the postage to Great Britain.