Date: Sun, 31 Mar 2019 08:12:24 +0200 From: Polytropon <freebsd@edvax.de> To: RW <rwmaillists@googlemail.com> Cc: RW via freebsd-questions <freebsd-questions@freebsd.org> Subject: Re: Why is Sendmail still around? Message-ID: <20190331081224.f6e4cf61.freebsd@edvax.de> In-Reply-To: <20190330145410.17cfd72d@gumby.homeunix.com> References: <4101a1092141b58e05ef7552278b15ff@kathe.in> <b6024975-31b1-e08b-46ee-e18597ada469@netfence.it> <b13d35f7472591ebd90c02d100b9ce80@kathe.in> <20190329121212.1f12fed7.freebsd@edvax.de> <20190329140110.3c7102ef876f3a1e58ea467b@sohara.org> <20190330034114.54ae2511.freebsd@edvax.de> <20190330145410.17cfd72d@gumby.homeunix.com>
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On Sat, 30 Mar 2019 14:54:10 +0000, RW via freebsd-questions wrote: > On Sat, 30 Mar 2019 03:41:14 +0100 > Polytropon wrote: > > > On Fri, 29 Mar 2019 14:01:10 +0000, Steve O'Hara-Smith wrote: > > > > I wouldn't attempt to run an outgoing mail server doing > > > direct MX lookup and delivery these days they anti-spam measures > > > are a nightmare. OTOH reliable delivery relays are not that common > > > either. > > > > Yes, it's not as easy anymore... You have to fight "we know better > > than you!" providers who consider every IP from a dynamic range > > a spammer, > > They pretty much have to. Most spam is caught by simple DNS based > tests which rely on assuming that no dynamic IP addresses sends direct > to MX. In particular most blocklists can't distinguish between a spam > source and a dynamic address, because an infected machine can cause > hundreds of dynamic addresses to be listed. Don't get me wrong - I fully understand that problem. But the attitude of mail operators who seem to consider every provider except themselves a spammer who has to "prove his worth" is annoying. Pwned "Windows" PCs that send tons of spam from their dynamic IP ranges tend to "pollute" whole subnets, so if you accidentally happen to be in the same range (belonging to the same provider or not), whatever you send is considered spam. You can ask to whitelist your IP, but you'll have to do this with almost every mail provider you want to contact, and as soon as you get a new dynamic IP, rinse repeat. Having access to a static IP often helps, but still some of the problems will stay... > These days spammers put a > lot of effort into compromising vulnerable servers, sometimes this > allows their spam to pass SPF, DKIM and even DMARC. Exactly thos emechanisms, intended to _prevent_ spam, can be used by spammers, so mail providers will happily accept their spam because the sender has successfully "proven his worth". If I remember correctly, more than 90% of today's messages transmitted across the Internet is spam, and of course spammers are interested in getting the "big guns" (corporate-class servers), but having access to a distributed network of pwned "Windows" home PCs is still useful for their purposes. > In some cases a home server with an MTA configured to use a smarthost > can be a gift to a spammer if it's compromised. Definitely. That's why securing the server properly and _not_ exposing a public open relay is very important. Due to my impressions and experience, I'd say the common UNIX guy is better at this as any HPC lurking in corporate IT. ;-) -- Polytropon Magdeburg, Germany Happy FreeBSD user since 4.0 Andra moi ennepe, Mousa, ...
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