# postfix and extreme high latency - Denial of service like

## centran

I am having a weird problem. When I have postfix running and accepting connection the latency on my machine goes through the roof. I get 1500+ ms pings to google and a bunch of lost packets. It is almost like a DOS.

I have deleted deferred mail in case that was causing a problem. I have checked that the machine isn't an open relay.

If I shut down postfix for awhile then latency goes back to normal for a couple of minutes.

tcpdump show a yahoo mail server continually trying to connect to me an insane amount of times.

IP mta-v1.mail.vip.sp2.yahoo.com.smtp > core.37121: . ack 136801 win 8280 <nop,nop,timestamp[|tcp]>

I doubt yahoo is trying to DOS me. Is there something wrong at there end? Is there something wrong my server might be doing?

Any help would be appreciated. Even a point in the right direction.

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## Ant P.

You could try contacting yahoo's abuse address about it.

Failing that, you could throttle or block them using iptables. Something like this:

```
iptables -N mailspam

iptables -A INPUT -p tcp --dport smtp --syn -s 98.136.0.0/14 -j mailspam

iptables -A mailspam -m limit --limit 2/min -j ACCEPT

iptables -A mailspam -j REJECT

```

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## centran

Good idea. I just threw them into hosts.deny for 5 minutes. It sopped after that.

I was just worried my machine might have sent some weird or garbled request or my machine wasn't acknowledging a request properly so they just kept sending.

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