Thank you. Michael, and also I appreciate  the advice I got offline which
was to allow only small pictures because a lot of people don't have the time
for slow
downloading if they don't have the latest equipment.

But the limit went way higher than what you are speaking of.  A 40 KB photo
took 880 lines.  I found that because I had put myself on review, and the
number of lines in a message will come up when it returns to you for
confirmation.

The Klez.H virus of 131K, that had been rejected and was sent to me as the
putative sender (I had not sent it), had over 1800 lines.  I set the limit
at 1000 lines, which allowed the image to transmit, but the Klez virus would
have been rejected.  Now I have a picture of 50.5 KB that  I will send in
the
next few days and I will temporarily change the limit to 1200 lines;
otherwise the limit will be a little over 40 KB at 1000.  I will try that
for a while.  I am generally relying on the attachment type in general with
the sizlim as something of a backup.

As for the suffix, I used JPEG as the application name, and advised the list
to use .jpg photos.  Only the first two have been posted, both with that
designation and with no difficulty.  Problems may lie in the future.

The comments I have from the list  are mostly from what you would call the
high-end, most knowledgeable birders who don't want to be bothered with
downloads at all.  But a list in my view should consider the less
knowledgeable, and ours is something like a one-room school. K-Ph.D in one
room.

If anyone knows more about viruses that they think I should know, I would
appreciate your sending it, either on or off the list.

Caveat:  Listserv sent a special digest when the two pictures had been sent,
and it came out in code, not in a picture.  I know digest does peculiar
things, and I had hoped it would filter the pictures.  I have an account of
mine set to digest so I can see how things are doing in that respect.  When
I saw the result,  I advised all of the 26 people on digest to set to index
and posted that to the general list as well.   As of now, only one from the
digest has made the change to index.  Most of the people on my list have not
had much experience with Listserv.  A few only.

I may be sitting on a time-bomb and just not know it.

Thanks for your help and I will leave the matter open for further comments.

Barbara Passmore


----- Original Message -----
From: "Michael Shannon" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Sunday, August 04, 2002 10:17 PM
Subject: Re: [LSTOWN-L] Limiting types of images - another try


> >
> > If I now delete the sizlim altogether, will the
> > Attachments=Images/jpeg be
> > strong enough to allow .jpg photos only, and not viruses?  I
> > am pretty sure
> > now that if I delete the size limit, the picture will be
> > allowed.  I don't
> > know however, how safe it is to rely on Attachments=Images/jpeg only.
> >
> > Can anyone take a chance and answer this?
> >
>
> OK, I'll take a stab.  :)
>
> Trying to limit on specific file types is something of a hit & miss
affair.
> I tried to do much the same thing with JPG & GIF files for one of our
busier
> lists a couple of years ago only to give up in frustration.  While most
mail
> clients will declare the attachments properly (eg. Content-Type:
image/jpg;
> name="image.jpg") not all of them do.  Plus (expecially in the case of
> JPGs), there is sometimes two extensions to think about (eg. JPG and JPEG)
> which adds to the problem.  I would imagine you would find out, as I did,
> that it will work for about 80% of your subscribership and not for the
rest
> (and according to Murphy's Law, it will undoubtedly be the most vocal
ones).
>
> Now, your question above asks if removing the size limitation will
> comprimise security.  In my opinion, I'd say, "Yes".  You said yourself
that
> you consider your current measures "trustworthy in avoiding viruses".  As
a
> certain member of this very list is wont to quote, "If it ain't broke,
don't
> fix it".
>
> If you *must* allow JPGs onto your list then I'd suggest modifying your
> thinking somewhat.  Keep your header as you've got it now:
>
> Language=noHTML
> Attachments=Images/jpeg
> Sizlim=210
>
> To make it easier to send pictures, increase your Sizlim= to something
like
> 250-300 lines.  I seem to recall that in my own testing this allowed up to
> 40kb filesize, which is plenty big enough for a picture.  Anything larger
> becomes unwieldy over SMTP.  Your subscribers will either have to live
with
> that or learn how to make a JPG file smaller (easy enough to do without
> losing quality if you know how).
>
> This also helps to block most viruses which seem to weigh in at around the
> 350-400 line limit.  This is assuming that virus writers haven't gotten
> smarter since I last looked.
>
> Hopefully this answers your question.
>
> --
> Chazzozz!!
>
> Michael Shannon
> Webmaster
> [log in to unmask]
>
> "Before you can grow old and wise you must first survive being young and
> stupid." - Ancient Proverb
>
> Note: Opinions expressed on this list are my own and do not reflect the
> views, opinions or position of my employer.  If swallowed, seek medical
> advice.