Outlook already has the option to download just the headers (if that is
what you meant by "head").  You can then select (mark) which messages to
download and then manually instigate the download of those marked
messages.  Having to mark and then manually download the marked messages
is a pain.  You could always turn off the preview pane and then enable
the AutoPreview mode which shows the first lines of each received e-mail
but only in plain-text.

That has nothing to do with paid guaranteed delivery.  That "service"
only ensures the e-mail gets into your mailbox, not that YOU get it into
your local e-mail client.  They only need to get the package at your
door to get paid for that delivery.  Whether you open your door to
accept the package or not won't change them getting paid for the
delivery.  If guaranteed delivery is not what you are talking about, no
one paying a spamming service knows how effect is the delivery rate.
They will pay the same whether their spam got delivered to one recipient
or to a million of them.  Whether the recipients read the spam has no
effect on the rates charged by e-mail delivery service providers.