How Does Mail Work? (Also, modems, cables, telebits, etc.)

[Alexis Rosen]

MATLEVAN at EKU (Jerry LeVan) writes:
>When I try to send mail, nothing happens, when I look
>into /usr/spool/mqueue I find the letter and a companion
>file, the companion file contains a message which is
>a complaint that it can't find the host.
>
>Does this mean that I have to "configure" sendmail
>(shudder...moan...) for each "uucp" connection?

Not exactly. If you have frozen your sendmail file by saying
"/usr/lib/sendmail -bz", the compiled version will always be used, and
it will not know about new uucp hosts. So, since frozen sendmail.cfs are
a good idea, you need to refreeze the cf every time you add a host to your
/usr/lib/uucp/L.sys file.

Of course, if your sendmail.cf isn't right to begin with, nothing will help
you...

>My SysV machines at work "know" immediately when I
>add a new uucp host an I don't have to "do" anything
>extra.

Either they aren't freezing their cfs or they're not running sendmail.
Or, perhaps, they are using a smart host as a forwarder, and it's up-to-date
or not running sendmail or not freezing its fc.

>I found the README file in /usr/lib/sendmail.cf referentially opaque.

Join the rest of the planet.

>UUnet sent me a flyer offering T2500's for about $895.00 and
>lower end models for what looked like reasonable prices.
>(Telebit Modems). Do the Telebits work well with A/UX? Will
>my Practical Peripherals 2400 modem cable work with the Telebits?

That's not a bad price, but I think I've seen $800 or so. Don't know where.

So far, a telebit is the _only_ modem I've managed to make work with A/UX
consistently over long periods. I've been experimenting with several
different sorts of 2400bps modems for the last two weeks and they're
driving me up a wall!!! I'm beginning to suspect that there may be some
flaw in A/UX, although I'm at a loss to explain how. What I do know is that
I've seen strange behavior that should be impossible, which goes away when
I reboot. On the other hand, some behavior is more persistent (and annoying!).

I do know of several (reliable) people who say they've gotten 2400s working
with A/UX. I don't know if they have put their modems through a level of
testing as rigorous as my experiments (perhaps they have).

So I can't definitively assign blame anywhere. At this point the only
definite thing is that I haven't gotten enough sleep in over a week :-( .

As for the cable, it all depends on what you want to do. The right cable looks
like this:
Mac (din 8)		Modem (db25)
------------------------------------
1: HSKo			20: DTR	(Data Term Ready- Mac is willing to take calls)
2: HSKi			 8: DCD	(Carrier Detect- Modem has a call waiting)
3: TxD-			 2: TxD	(Transmit Data- negative half of balanced pair)
4: GND			 7: Sgnd (Signal ground)
5: RxD-			 3: RxD (Receive Data- negative half of balanced pair)
6: TxD+			--n/c--
7: GPi (or n/c)		--n/c--
8: RxD+			 7: Sgnd (alternatively, tie RxD+ to 4 on the Din-8)

The explanations for DTR/DCD are fuzzy but useful, when the modem is set up
for incoming calls. It that case, the modem line must be in "modem" mode.
If you want to dial out with A/UX, you'll have to do a "stty -n /dev/ttyxx
 -modem", but I think telecom is that last thing on earth I'd want to do with
A/UX. Use a Mac app instead- I think all the standard ones work fine with
A/UX.

For dialout only, I think you could get by without HSKo and HSKi.

>Do the Telebits work well at 2400 baud. (The main campus modem
>pool is 2400 and less.

They have no problem, and speak MNP up to 5 (older ones up to 4, I think).
I have notiecd however that, when I call a 2400bps modem on an A/UX box,
from my MacOS Mac with a Telebit TB+, it doesn't quite manage to sync with
the other modem right away. I have to hit dozens of breaks and returns to
get in sync. Once this happens, though, it performs perfectly. It's also not
true of several other 2400bps modems on other systems (such as two modem
pools I occasionally call).

>I also have Paul Campbell's CommCard, is it more efficient
>to use a "fast" modem with the ports card?

Very much so. Especially if you're doing uucp transfers. Without this card,
a Telebit would bring your Mac to it's knees in short order. (Why doesn't
Apple mention 'knees' on their list of things that come with the Mac? They
see a lot of abuse... :-)

Don't forget to do "/etc/t_modem /dev/ttyxx uucp" (or something like that-
check the mac page) in order to enable the special uucp mode on this card,
for each port that handles uucp. It doesn't interfere with regular serial
i/o.


Now it's my turn to cry for help. If anyone can tell me what's wrong with
my modems, I'll be very grateful. Help!!!

---
Alexis Rosen
Owner/Sysadmin, PANIX Public Access Unix, NY
{cmcl2,apple}!panix!alexis