Re: Postfix-Server behind a DSL-Router

On 04/09/2015 12:46 PM, Peter Ulrich Kruppa wrote: > > Am 09.04.2015 um 21:30 schrieb Mike Wright: >> >> You can try running tcpdump to watch incoming connections while you send >> yourself an email from gmail/yahoo etc. That will let you know if mail >> is arriving and getting through your firewall. >> >> tcpdump -i eth0 port 25 (assuming single ethernet card). > This is, what I see, when an mail from outside arrives: > # tcpdump -i enp4s6 port 25 > tcpdump: verbose output suppressed, use -v or -vv for full protocol > decode > listening on enp4s6, link-type EN10MB (Ethernet), capture size 262144 > bytes > 21:39:21.951957 IP mail-wi0-f177.google.com.35438 > pukruppa.de.smtp: > Flags [S], seq 4222003974, win 42900, options [mss 1418,sackOK,TS val > 1017047302 ecr 0,nop,wscale 7], length 0 Yes. Between these two there should have been a reply from you, pukruppa.de.smtp > mail-wi0-f177.google.com.35438. > 21:39:22.951335 IP mail-wi0-f177.google.com.35438 > pukruppa.de.smtp: > Flags [S], seq 4222003974, win 42900, options [mss 1418,sackOK,TS val > 1017048302 ecr 0,nop,wscale 7], length 0 > > Does that say anything to you? > Which side of your router are you listening on, public or private?

If it's the public side that only shows that mail and dns are working from outside. Now you have to test from inside. If it's the private side it says mail is making through and your mail server is not answering.