Can originating IP addresses be faked?

[David Fletcher]

Although I know a little bit about networking I'm not an expert and
certainly know nothing about hacking other peoples' computers. Some
people have told me that IP addresses can somehow be faked like the
jerks who make nuisance phone calls faking their number to make it
appear to be a friend, the bank, etc., calling.

Can I for example be confident that these relay attempts:-
Jul 24 11:31:57 ServerIII postfix/smtpd[22736]: NOQUEUE: reject: RCPT
from hwsrv-294731.hostwindsdns.com[142.11.195.132]: 454 4.7.1
<1029mandaditos at gmail.com>: Relay access denied;
from=<killer at virginm.net> to=<1029mandaditos at gmail.com> proto=ESMTP
helo=<hwsrv-294731.hostwindsdns.com>
Jul 24 11:31:58 ServerIII postfix/smtpd[22738]: NOQUEUE: reject: RCPT
from hwsrv-294731.hostwindsdns.com[142.11.195.132]: 454 4.7.1
<1029mandaditos at gmail.com>: Relay access denied; from=<love at virginm.net>
to=<1029mandaditos at gmail.com> proto=ESMTP
helo=<hwsrv-294731.hostwindsdns.com>
Jul 24 11:31:59 ServerIII postfix/smtpd[22736]: NOQUEUE: reject: RCPT
from hwsrv-294731.hostwindsdns.com[142.11.195.132]: 454 4.7.1
<1029mandaditos at gmail.com>: Relay access denied;
from=<sunshine at virginm.net> to=<1029mandaditos at gmail.com> proto=ESMTP
helo=<hwsrv-294731.hostwindsdns.com>

which are a small sample from around 300 really did originate from
Hostwinds, Washington, USA?

Thanks for your advice, all.

Dave