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Root to bind ports under 1024?
A better round-robin DNS server
Postfix Antispam
HOWTO: Linux and iSCSI
VPN two computers together with Wireguard
Gaming in the cloud
Share storage over a network
Enjoyable development
When things go wrong on Linux
Email blacklists
Missing the point of SPF
Offsite backup with iSCSI
jconsole remote connections
YouFibre
PFS in Firefox
Jesus saves, but Buddha makes incremental backups
Stream your CD collection to work
Cookies
On-demand streaming audio server
rm strcpy
Aaargh - more J2ME stupidity
How to update your Nokia N80 to the N80 Internet Edition firmware
Let a friend use your IP address to get access to a machine that you can access, but he can't
Erlang
Apache vs nginx?
Acer TravelMate 5720 4GB running Linux
Running out of IPv4 address space?
systemd
Reverse firewall
Playing with software defined networking
Peer's certificate has an invalid signature. (solved)
IPv6
How to run two instances of Tomcat on your machine
Linux driver support

Comments


Of course, there'll always be some mail servers that don't follow the RFCs properly. Checking the logs, I noticed the following: Sep 26 03:11:47 hosting postfix/smtpd[19263]: connect from mail7.exchange.microsoft.com[131.107.1.27] Sep 26 03:11:49 hosting postfix/smtpd[19263]: NOQUEUE: reject: RCPT from mail7.exchange.microsoft.com[131.107.1.27]: 450 4.7.1 : Helo command rejected: Host not found; from= to= proto=ESMTP helo= Sep 26 03:11:49 hosting postfix/smtpd[19263]: disconnect from mail7.exchange.microsoft.com[131.107.1.27] Now, according to the SMTP RFC (http://www.ietf.org/rfc/rfc2821.txt): The domain name given in the EHLO command MUST BE either a primary host name (a domain name that resolves to an A RR) or, if the host has no name, an address literal as described in section 4.1.1.1. So why isn't there a DNS entry for df-gwy-07.exchange.corp.microsoft.com? Anyway, to allow these broken setups to skip the "reject_unknown_hostname" in "smtpd_helo_restrictions", (as I don't want to disable it - it catches 95% of the spam) - you need to do the following: * In main.cf, add parent_domain_matches_subdomains = yes * In the smtpd_helo_restrictions section, add "check_helo_access hash:/etc/postfix/helo_access" * In that helo_access file, list the offending "HELO/EHLOs" - in this case: .exchange.corp.microsoft.com OK * Finally, run postmap /etc/postfix/helo_access to build the DB file, and restart postfix. It does appear to be a problem more with some mail server admins than others. (https://www.nearlyfreespeech.net/about/email.php#software)