Can't spammers bypass this check by just faking a real domain name in the FROM: field, something like s...@gmail.com?
> -----Original Message----- > From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On > Behalf Of David Boyes > Sent: Monday, January 23, 2017 6:20 AM > To: IBM-MAIN@LISTSERV.UA.EDU > Subject: HMC Mail domain > > >I don't understand, do you mean > >add another MX and A record at > >the company site domain server, > > In yours. The root problem is actually a good thing - modern mail systems require that the > sending domain name actually resolve to something to prevent spammers. Otherwise, the > SMTP protocol allows you to put literally anything in the MAIL FROM: part of the > transaction. It's possible to turn this feature off by changing the source (it's one of the things > in the 'dontblamesendmail' options) but it is a Very Bad Idea. > > As long as the receiving system can resolve whatever the sending system says to > *something*, you're good. Thus, an entry in your DNS like this: > > Hmc1 in a 192.168.0.1 > In mx your.mx.server > > will fix it. You don't have to actually be able to connect to it; the name just has to resolve. > > (In case you care, the error message you posted has only one cause. In the last few years, > almost all mail systems have required the sending system to be in DNS to prevent spammers > on the theory that it's generally harder to spam if you have to take the step of registering in > DNS before you start sending out mail. The NXDOMAIN message is telling you that the > receiving system cannot find the sending system in DNS (non-existent domain) so it's > bailing.) > > In general, make a practice of putting everything that gets an IP address into DNS, even if > you're using DHCP. It's been 35+ years since DNS was invented; it's time. > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
