On the web pages listed under the dmoz link you find quite a couple of explanations for what a Class A Address, a Class B Address, or a Class C Address is, this may be the tersest one you may find, but it's here for my own reference:

But I like esp. the one I found in the O'Reilly book on TCP/IP Network Administration, chapter 2, named “Delivering the Data”, in the section named “The IP Address”, subsection “Address Classes”.

		$ 
		cd ~/tmp/xfer

		# -D is a bit like tar's --directory,
		#     but it's still used as leading path;
		# -T makes smbclient behave a bit like tar,
		#     the c afterwards is tar's --create
		#     the letters afterwards are meant to behave like tar's operation modifiers,
		#     g makes smbclient only transmit files
		#         that have the archive bit set,
		#     a resets that archive bit on the Win98 box
		#         after retrieving the file from there;

		smbclient //hayek6/c -N -Tcga - money 2>/dev/null | tar xvf -
		smbclient //hayek6/c -N -Tcga - home  2>/dev/null | tar xvf -

		# POST: this actually also retrieved the entire directory structure from remote;

		# we want to get rid of empty directories:

		find . -depth -type d -empty -exec rmdir '{}' \;

		# find the files:

		find . -type f

		# ... and move them to their respective places;

		$ 

		# all the files copied won't get their original modification date/time, although the manual page says so,
		# and they all also get the archive bit said, which is quite some rubbish;
		# I haven't found a way to avoid all that yet;

		cd ~
		tar cf  - money                                                                                 | smbclient //hayek6/c -N -Tx -

		cd /export
		tar cf  - home/jochen_hayek/{diary,etc/{addr.s-exp,passwords}}                                  | smbclient //hayek6/c -N -Tx -

		# this will (amongst other things) reset all archive bits:

		smbclient //hayek6/c -N -Tcga - home > /dev/null

If your computer's access to the Internet is not continuous, you will have to retrieve your e-mail from your mail host via an IMAP (and/or POP) capable client software. I'm using fetchmail. The author: @cite{[Eric_S_Raymond]} and his community. He presented an article on its development: The Cathedral And The Bazaar.

A protocol to access and manipulate e-mail on dedicated servers. I have written a utility in the python programming language to handle my incoming e-mail in my IMAP INBOXes (there is one INBOX per account). After moving messages from an INBOX to a dedicated mail folder, The e-mail than gets downloaded selectively using fetchmail. The expected URL: www.IMAP.org.

imap stream tcp nowait root /usr/sbin/tcpd /usr/bin/ssh -p 443 -USER@HOST /usr/sbin/imapd

See `IMAP'! POP is the `older' version of IMAP, to explain it in very simple words.

There is much to say about SMTP, but currently I only write down here, what I need to handle my e-mail forwarding on ACM.org (a VMS host);

		  $ mail

		  MAIL> set  forward in%"""...@@..."""

		  MAIL> show forward
		  Your mail is being forwarded to IN%"...@@...".

		  MAIL> set  noforward

		$ testhost $NNTPSERVER -a -T 300 > active-$NNTPSERVER-UNSORTED # give it much longer to time out, because it's so busy ...

		# maybe the result of $(date '+%s') instead of 999 :
		cat /var/lib/news/history ~jo_hayek/.nnmail-cache |
		perl -ne 'm/^<(.*)>/ && print "<$1>\n"' |
		sort -u |
		perl -ne 'chop; print $_,"\t999~\n"' > /var/lib/news/history-NEW

		# SuSE's suck just uses flat file history, so this is not worth while at all;
		# hence I don't need inn's makehistory at all, and hence no fake inn installation:
		/usr/lib/news/bin/makehistory -or # IN: /var/lib/news/history; OUT: /var/lib/news/history.{dir,pag}

		$ cd /home/jochen_hayek/NNTP-suck

		# maybe you want to add:
		#     --cleanup -> sucknewsrc, sucknewsrc.old, suck.newsrc

		suck ${NNTPSERVER} --postfix -${NNTPSERVER} --cleanup > NEWSBOX-${NNTPSERVER}
		suck ${NNTPSERVER} --postfix -${NNTPSERVER}           > NEWSBOX-${NNTPSERVER}

		#     $(perl -ane 'print "--ng $F[0] \n"' sucknewsrc-TEMPLATE )

		JHparse_news_batch.py --verbose \
		    $(sed 's/^\([^ ]*\).*/--ng \1/' sucknewsrc-${NNTPSERVER}) \
		    NEWSBOX-${NNTPSERVER}
		# POST: leaves the articles in subdir ./tmp

		cd tmp; \
		for i in *
		do  echo "$i":
		    cat "$i" >> ~/procmail-dir/"$i" && rm "$i"
		done

		##########

		suck ${NNTPSERVER} --postfix -${NNTPSERVER} --timeout 300 --dir_msgs ${NNTPSERVER} --batch_lmove lmove.cf-${NNTPSERVER}

		$ 
		perl -ane 'print $F[0],"\n"' sucknewsrc-*.?? | sort -u | sed 's/$/ 0/' > sucknewsrc-TEMPLATE

		for i in sucknewsrc-*.??
		do  : echo $i:
		    perl -ae '

			while(<>) { @F=split; $high{$F[0]} = $F[1]; };
			foreach(sort keys %high) { print "$_ $high{$_}\n" }

		      ' sucknewsrc-TEMPLATE "$i" > "$i-NEW"
		    cmp -s "$i" "$i-NEW" || echo "*** $i: needs updating"
		done

		rename 's/-NEW$//' sucknewsrc-*.??-NEW

		$ 
		suck "$1" -bl /var/lib/news/active-"$1" -c

		# in exactly this order, because the 2nd pass does the clean up:

		find ..... -type f | while read i; do fgrep -il base64 $i && munpack "$i" && rm -f "$i"; done

		find ..... -type f | while read i; do echo "$i":; uudecode "$i"; rm -f "$i"; done

Used by ADSL providers, e.g. by Deutsche Telekom for their product T-DSL.

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This method has been used for quiet a while within SuSE Linux by the utilities wvdial, kppp, smpppd, ..., as they have their own places for keeping PPP accounts and passwords. Not that this is safer than keeping that in pap-secrets or chap-secrets, but at least accounts and passwords are only kept in that one place preferred by the respective utility.

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