postfix fails to install/upgrade with error exit status 75: invalid hostname configuration

This is not a package bug, but the package correctly responding to a bad configuration in your system:

Running newaliases
newaliases: warning: valid_hostname: invalid character 32(decimal): PARENTS PC
newaliases: fatal: file /etc/postfix/main.cf: parameter myhostname: bad parameter value: PARENTS PC
dpkg: error processing postfix (--configure):
 subprocess installed post-installation script returned error exit status 75

I'm converting this bug report to a support question so you can get help setting a valid hostname.

Change your hostname (i.e., the name of your computer) to something without a space (also no punctuation and no leading numeral, but you already don't have those things). ParentsPC or PARENTSPC would work.

One way to change your hostname is to edit /etc/hostname. See http://www.ducea.com/2006/08/07/how-to-change-the-hostname-of-a-linux-system/ (go down to "Permanent hostname change on Debian based systems") for details.

I had noticed some suggestive "fix" comments on various sites and even did an rm on /usr/sbin/postfix but that didn't work either ---
(Of course, before that, I had tried the conventional apt remove and purge commands on it as well --- The log I've enclosed below is probably the same as others (who have had a similar problem) but thought I'd include (FYI) ---
Also, I noticed that in /etc/postfix/main.cf that the system was "barking" at myhostname (bad parameter value) -- Is that something I could edit that file to correct it ? -- Just a thought or suggestion --

===============================================
Running newaliases
newaliases: warning: valid_hostname: misplaced delimiter: jmccormi-Studio-1558..
newaliases: fatal: file /etc/postfix/main.cf: parameter myhostname: bad parameter value: jmccormi-Studio-1558..
dpkg: error processing package postfix (--configure):
 installed postfix package post-installation script subprocess returned error exit status 75
Processing triggers for libc-bin (2.32-0ubuntu6) ...
Errors were encountered while processing:
 postfix
E: Sub-process /usr/bin/dpkg returned an error code (1)
===============================================

Thanks, John McCormick --- Email: <email address hidden>

I also have a hunch that if you could prompt (at "update-manager" time) my OS to a Partial Upgrade and I would like to have that happen because it prompted me already and I failed to make that upgrade --- it's possible, if you gave me another chance to do this "Partial Upgrade" that this problem might fix itself -- (In other words, please give me a way to trigger a "partial upgrade" as I would be curious to know if that might automatically fix this postfix problem
=====
John McCormick
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Email: <email address hidden>