Make mboxgrep recognize dates

Did a Google search "mboxgrep dates" and https://trisquel.info/en/forum/make-mboxgrep-recognize-dates
was at the top of the list.
A little farther down in the Google search was an item about grepmail:
https://packages.debian.org/buster/grepmail
See also: https://metacpan.org/pod/grepmail
Available from the Trisquel repository but not included in Add/Remove Applications
Install with apt-get ... man pages have lots of detail.
First try:
grepmail -u -f Dates.from.Emails.no.Dates.txt 1998-2022.Newest > First-grepmail-search.txtTook 18 seconds.
Proof:
grep "From -" First-grepmail-search.txt | sed 's/From\ -\ //g' > Check-Pattern-Matches-grepmail.txt ;
comm -12 <(sort -k 1,1 Dates.from.Emails.no.Dates.txt) <(sort -k 1,1 Check-Pattern-Matches-grepmail.txt) > Dates-Common-to-Both-Files-grepmail.txt ;
comm -23 <(sort -k 1,1 Dates.from.Emails.no.Dates.txt) <(sort -k 1,1 Check-Pattern-Matches-grepmail.txt) > Dates-missed-by-grepmail.txt
Grepmail appears to have a lot of promise for use in my spam project.

the syntax escapes me.

$ date -d 'Fri, 01 Feb 2019 00:07:49 -0800' +%c
Fri Feb 1 06:07:49 2019

Continuing to account for all the emails in 1998-2022.Newest:

Steps to account for every email:
LC_ALL=C ./MB-Scrape-Emails-GL-PO 1998-2022.Newest | sed 's/\t\t/\tnull\t/g' > Hairball-1998-2022.Newest.txt 19.3 MB
Gathers all 10308 of the individual emails. Takes about six seconds; 19.3 MB.
head -n 1 Hairball-1998-2022.Newest.txt | sed 's/\t/\n/g' | sed 's/:/\t/g' | sed 's/\#\ //g' > Headers-1998-2022.Newest.txt
Lists the headers of the numbered columns in the email summary:
1 Content analysis details
2 Date
3 Delivery-date
4 IPv4-addr-in-contents
5 IPv4-addr-in-headers
6 Message-ID
7 Return-Path
8 Subject
9 URL-in-contents
10 URL-in-headers
11 X-Account-Key
12 X-Spam-Score
13 X-UIDL
14 email-addr-in-contents
15 email-addr-in-headers
16 email-addr-with-at-in-contents
17 email-addr-with-at-in-headers

cut -f 2,13 Hairball-1998-2022.Newest.txt | awk -F '[\t]' 'NR -1 {print $2"\t"$1}' | sort -nk 1,1 > X-UIDL.and.Date.txt
Took half a second; has a couple of malformed lines at the beginning, 10277 OK, 25 nulls in Col.$2, and four malformed Col.$1 at the end ==> 2 + 10277 + 25 + 4 = 10308, totaling 19.3 MB. These thirty-one malformed sets of email data need further analysis.

grep "null" X-UIDL.and.Date.txt | grep "UID" | awk '{print $1}' > UID-pattern.txt <== use this as a starting point to grepmail those 25 dates.

grepmail -u -f UID-pattern.txt 1998-2022.Newest > Emails-UID-null.txt ==> 1.1 MB <== Twenty-five emails containing the target UIDs.

LC_ALL=C ./MB-Scrape-Emails-GL-PO Emails-UID-null.txt | sed 's/\t\t/\tnull\t/g' > Hairball-UID-null.txt <== MB's script-summary: Twenty-five dates, 18 of them in Col.$2, the other seven in Col.$3.

sed 's/\ /\\ /g' X-UIDL.and.Date.txt | grep -v "UID" | awk -F '[\t]' '{print $2}' > Six-strung-out-dates.txt
'Wed,\ 13\ Jan\ 2021\ 00:14:24\ -0700'
'18\ Apr\ 2019\ 12:21:15\ +0300'
'Thu,\ 24\ Jun\ 2021\ 18:09:36\ +0200'
'Thu,\ 24\ Jun\ 2021\ 18:05:29\ +0200'
'Fri,\ 03\ Sep\ 2021\ 05:10:55\ +0200'
'Fri,\ 03\ Sep\ 2021\ 06:25:11\ +0200'

Unsuccessful short-form script:
while read pattern
do grepmail -e $pattern 1998-2022.Newest > Mailbox-Six-Dates.txt
done < Six-strung-out-dates.txt Saved as Script-Mailbox-Six-Dates.txt but fails.

Fall back to GL's longform technique, which is constructed on the Leafpad platform: ==>
grepmail -u 'Wed\, 13\ Jan\ 2021\ 00:14:24\ \-0700' 1998-2022.Newest >> Emails.Found.by.grepmail-Escaped-pattern.txt ;
grepmail -u '18\ Apr\ 2019\ 12:21:15\ \+0300' 1998-2022.Newest >> Emails.Found.by.grepmail-Escaped-pattern.txt ;
grepmail -u 'Thu,\ 24\ Jun\ 2021\ 18:09:36\ \+0200' 1998-2022.Newest >> Emails.Found.by.grepmail-Escaped-pattern.txt ;
grepmail -u 'Thu,\ 24\ Jun\ 2021\ 18:05:29\ \+0200' 1998-2022.Newest >> Emails.Found.by.grepmail-Escaped-pattern.txt ;
grepmail -u 'Fri,\ 03\ Sep\ 2021\ 05:10:55\ \+0200' 1998-2022.Newest >> Emails.Found.by.grepmail-Escaped-pattern.txt ;
grepmail -u 'Fri,\ 03\ Sep\ 2021\ 06:25:11\ \+0200' 1998-2022.Newest >> Emails.Found.by.grepmail-Escaped-pattern.txt ;Saved as Script-Mailbox-Six-Dates-longform.txt
./Script-Mailbox-Six-Dates-longform ==> Took 5.624 seconds; 150.9 kB
LC_ALL=C ./MB-Scrape-Emails-GL-PO Emails.Found.by.grepmail-Escaped-pattern.txt | sed 's/\t\t/\tnull\t/g' > Hairball-Six-Dates-longform.txt Lists the original six dates in Col.$2.
This series of step thereby enables MB's main script to summarize all of the Emails in 1998-2022.Newest.