Unclear on argument passing to "sendmail'

[Tim Williams]

On 22/08/06, Tim Roberts <timr at probo.com> wrote:
> John Draper <lists at webcrunchers.com> wrote:

Hi Tim :)

> Tim William's answer is not exactly correct.  The host you specify in the
> smtplib.SMTP constructor should NOT be the MX record for any of the
> recipients.  You should never have to look up MX records yourself.

actually, I said:
this will be a server from the recipient's domain's mx records (or
your ISP server).  :)

However it really depends on the use-case,   relaying through another
server will give you no control over bad addresses,  you have to wait
for bounces from the recipient's server,  or conversely the ISP server
can give fails 4xx & 5xx for valid addresses.   The ISP may only
accept email addressed from their local domains, and you may be
breaking their TOCs or AUP and get blocked.

On the flip side, some ISPs block outbound port 25 except through
their servers, or transparent proxy port 25,  so Direct MX is
unusable.

Blacklists are hit and miss, even large ISPs can get listed.  If you
are on a "clean" range then it shouldn't matter, you can look up your
IP on various blacklists to see if it is affected.  Also Many fixed IP
addresses don't have valid PTRs so they can fail as often as dynamic
IP addresses which usually do have valid PTRs

 John Draper <lists at webcrunchers.com> wrote:

> Hmmm - the problem I have is if I knowingly
> put in a bad recipient,  and try to send to a
> unknown user,  I get all appearances that
> the mail went through.

Yes this will happen if you use a relay server.

> Ok,   so If I already have a MX hostname
> of "mail.myhost.com",  then I would put
> into my "to_email"...    <myusername>@myhost.com for

Yes,  if you just used username the server wouldn't know which domain
the email was being sent to and therefore how to route it.

> By the way,  I'm sending this mail to a "sms"
> gateway to a cellular provider, so the
> username is their phone number.

If you only ever send to this gateway then you might as well try MX
records, you will have more control,  but you will need to manage
queueing yourself for temporary failures,  or you may decide that if
you get a temporary failure (4xx) to just fire the email off to your
ISP server and let them deal with it.


> But
> (sigh),  these providers don't appear
> to tell me if I put in a bogus phone number.

Unfortunately not all mail servers will fail an invalid address even
if they aren't relaying the email.   But in this case the SMS
"gateway" is probably relaying to a backend system for the SMSc and
will accept any address with a valid domain part.

HTH :)