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  1. #1
    Linux Newbie SagaciousKJB's Avatar
    Join Date
    Aug 2007
    Yakima, WA

    Misunderstanding mail protocols

    Well, I'm trying to setup a home email server, and I'm using Postfix and openwall popa3d for my pop3 and smtp server. The smtp server sends fine, but I didn't want to even risk spammers using it, so I closed it off to the outside world. For some strange reason, this prevented me from actually receiving mail on pop3. I couldn't figure this out until I tried sending mail through gmail, and watched my shorewall log at the same time. I caught this

    ...SRC= DST= LEN=60 TOS=0x00 PREC=0x00 TTL=48 ID=14198 PROTO=TCP SPT=56212 DPT=25 WINDOW=5720 RES=0x00 SYN URGP=0
    Having IPWhois'd GoogleBot a few times, I instantly recognized the SRC as Google, and realize that for some reason, it had to connect to SMTP to send mail to me. So, I opened up SMTP to the outside world, and everything works now.

    This goes against everything I know about email, which really isn't that much anyway. I'm wondering if this is right, or if there is a problem here. I wouldn't think I'd need SMTP open to receive mail to my POP3 server, but without SMTP being open, nothing will get through.

    Secondly, if I really do need SMTP to be open, what's the best way to harden it to prevent spammers using it?

  2. #2
    Linux Newbie athlon_crazy's Avatar
    Join Date
    Sep 2007
    SMTP=MTA=Mail Transfer Agent. No mail will be transfered without it!

    Basically, just make sure you smtp is not open for relay. U can test it here Check an Open Relay

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