Thank you, Jon. That clears it up considerably, even though you've told me there is no single correct answer (Sendmail may try several servers according to some scheme).
I don't think my ISP limits my communication through my node on the Internet; I've got a dynamically assigned IP address. I seem to be able to telnet to port 25 of most any mail server, and at least attempt an SMTP exchange. Rich Jon Carnes wrote: > > On Mon, 2002-09-30 at 13:18, Richard O. Hammer wrote: > > I am working on a service which needs to send SMTP messages. > > With all the concern about improper forwarding of email > > messages, I want to know: to which SMTP server is it proper > > for me to send a given message? > > If you are working from a internet connection where the ISP limits the > forwarding of SMTP, then you will need to use the ISP's SMTP servers... > Most user based ISP's do block SMTP at the border. If they provide a > business class solution, then they may or may not also allow you > straight access to other smtp servers that are off of their net. > > This is a royal pain to business folks that travel. The best solution > is to use Authenticated SMTP (on a high port). > > > > (Here is a similar question, worded another way) When Sendmail > > sends a message to [EMAIL PROTECTED], does it: > > 1) query which mailserver serves dog.org, and then connect to > > that mailserver to send rover's message? or > > 2) connect to a mailserver run by the ISP, from which this > > Sendmail-hosting organization buys its Internet connection, > > and send the message to [EMAIL PROTECTED] through that server? > > By default Sendmail does a DNS based MX lookup to find the proper > mailserver, and then attempts a direct connection. If that fails, it > moves on to the secondary. Most small/medium businesses use their ISP's > mailservers as a secondary (or tertiary). > > So the mail may not be delivered directly, but sendmail does find a > responsible party to handle the mail. > > If a company is running off an SMTP restrictive ISP and the company does > not arrange for the ISP to act as an SMTP secondary, then Sendmail will > most likely not be able to deliver the mail. > > You can of course, set sendmail to use the ISP's SMTP servers as relays. > > Jon > > _______________________________________________ > TriLUG mailing list > http://www.trilug.org/mailman/listinfo/trilug > TriLUG Organizational FAQ: > http://www.trilug.org/~lovelace/faq/TriLUG-faq.html _______________________________________________ TriLUG mailing list http://www.trilug.org/mailman/listinfo/trilug TriLUG Organizational FAQ: http://www.trilug.org/~lovelace/faq/TriLUG-faq.html
