Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!news.glorb.com!news-xxxfer.readnews.com!news-out.readnews.com!transit4.readnews.com!panix!not-for-mail From: Grant Edwards Newsgroups: comp.lang.python Subject: Re: Simple Python script as SMTP server for outgoing e-mails? Date: Mon, 22 Jul 2013 14:10:00 +0000 (UTC) Organization: PANIX Public Access Internet and UNIX, NYC Lines: 40 Message-ID: References: NNTP-Posting-Host: dsl.comtrol.com X-Trace: reader2.panix.com 1374502200 21373 64.122.56.22 (22 Jul 2013 14:10:00 GMT) X-Complaints-To: abuse@panix.com NNTP-Posting-Date: Mon, 22 Jul 2013 14:10:00 +0000 (UTC) User-Agent: slrn/1.0.1 (Linux) Xref: csiph.com comp.lang.python:51042 On 2013-07-22, Gilles wrote: > On Sun, 21 Jul 2013 21:01:09 +0000 (UTC), Grant Edwards > wrote: >>Unless you've got a static IP address, a domain name, and a valid MX >>record that will match up when they do a reverse DNS lookup, it's >>pretty unlikely that you're going to have much luck running an SMTP >>server. Most other SMTP servers are probably going to ignore or >>reject your attempts to transfer mail from your own SMTP server. > > Incidently, how do ISP MTAs find whether the remote MTA is legit or > running on some regular user's computer? > > 1. Query Reverse DNS for IP > 2. Find domain > 3. Query DNS for MX > 4. ? There are a variety of things they check. They've got lists of IP address blocks that they know are residential DSL/cable customers, and sometimes they'll reject mail from those regardless of what you do. Some will compare the reverse-DNS lookup with the headers to make sure you're being honest about things like return-path, some will compare the IP address with the MX record for the domain they got when they did the reverse-lookup-DNS, and they've all probably got a variety of other secret heuristics they use to generate a "SPAM" score. For many years I ran my own SMTP server and had it configured to deliver mail directly to recipients. About 10 years, I had to give up on that because so many SMTP servers were rejecting/ignoring mail I sent. And I did have a static IP with a valid domain and MX record. But it was a residential DSL IP address, and I suspect that was enough to get mail rejected by some servers. -- Grant Edwards grant.b.edwards Yow! Well, O.K. at I'll compromise with my gmail.com principles because of EXISTENTIAL DESPAIR!