OPTIONS="-4" in /etc/sysconfig/named

Yes, postfix.

Hmmm, I'm monitoring the logs and nothing has changed, but you suspected that :)

I'm getting thousands of what look like fake 'to' email address in maillog. My server passes all the 'relay check' tests I can find, I don't think this is a relay issue... not positive though.

I don't know if these 'to' addresses have bcc addresses that are going to users on my server, or if one of my users has a virus on their desktop and is sending these out unknowingly. I don't know enough about reading these to understand - but it would appear we are sending these out.

Here's an example:

(my-ip-was-here) 26 17:51:59 julia postfix/smtp[11660]: 2E38C8C09D: host mx00.gmx.net[213.165.67.114] refused to talk to me: 421-gmx.net (mxgmx006) Nemesis ESMTP Service not available 421-Service unavailable 421-Reject due to policy violations. 421 For explanation visit http://postmaster.gmx.com/en/error-messages?ip=216.119.158.65
(my-ip-was-here) 26 17:51:59 julia postfix/smtp[11486]: 1D21866B04: host mta5.am0.yahoodns.net[66.196.118.36] refused to talk to me: 421 4.7.0 [TS01] Messages from 216.119.158.65 temporarily deferred - 4.16.55.1; see http://postmaster.yahoo.com/errors/421-ts01.html
(my-ip-was-here) 26 17:51:59 julia postfix/error[11571]: 2D5F5D4A69: to=<carlosmay17@yahoo.com>, relay=none, delay=118080, delays=118080/0.05/0/0.04, dsn=4.7.0, status=deferred (delivery temporarily suspended: host mta5.am0.yahoodns.net[98.138.112.37] refused to talk to me: 421 4.7.0 [TS01] Messages from 216.119.158.65 temporarily deferred due to user complaints - 4.16.55.1; see http://postmaster.yahoo.com/421-ts01.html)
(my-ip-was-here) 26 17:51:59 julia postfix/qmgr[11330]: 40C7416F5C5: from=<>, size=4164, nrcpt=1 (queue active)
(my-ip-was-here) 26 17:51:59 julia postfix/error[11571]: 2D5F5D4A69: to=<okinyisikinisamuel@yahoo.com>, relay=none, delay=118080, delays=118080/0.05/0/0.08, dsn=4.7.0, status=deferred (delivery temporarily suspended: host mta5.am0.yahoodns.net[98.138.112.37] refused to talk to me: 421 4.7.0 [TS01] Messages from 216.119.158.65 temporarily deferred due to user complaints - 4.16.55.1; see http://postmaster.yahoo.com/421-ts01.html)
(my-ip-was-here) 26 17:51:59 julia postfix/qmgr[11330]: 9B4C51FEF8C: removed
(my-ip-was-here) 26 17:51:59 julia postfix/error[11571]: 2D5F5D4A69: to=<t.bean252@yahoo.com>, relay=none, delay=118080, delays=118080/0.05/0/0.1, dsn=4.7.0, status=deferred (delivery temporarily suspended: host mta5.am0.yahoodns.net[98.138.112.37] refused to talk to me: 421 4.7.0 [TS01] Messages from 216.119.158.65 temporarily deferred due to user complaints - 4.16.55.1; see http://postmaster.yahoo.com/421-ts01.html)
(my-ip-was-here) 26 17:51:59 julia postfix/error[11529]: 1347776C2B: to=<geauxk@yahoo.com>, relay=none, delay=132611, delays=132610/0.11/0/0.05, dsn=4.7.0, status=deferred (delivery temporarily suspended: host mta5.am0.yahoodns.net[98.138.112.37] refused to talk to me: 421 4.7.0 [TS01] Messages from 216.119.158.65 temporarily deferred due to user complaints - 4.16.55.1; see http://postmaster.yahoo.com/421-ts01.html)
(my-ip-was-here) 26 17:51:59 julia postfix/qmgr[11330]: 1518D379BD: from=<tami@mysite.org>, size=685, nrcpt=9 (queue active)
(my-ip-was-here) 26 17:51:59 julia postfix/qmgr[11330]: 259C1110392: from=<tami@mysite.org>, size=805, nrcpt=4 (queue active)
(my-ip-was-here) 26 17:51:59 julia postfix/error[11570]: 2E47A8714B: to=<blake.cuny@yahoo.com>, relay=none, delay=129357, delays=129356/0.07/0/1.2, dsn=4.7.0, status=deferred (delivery temporarily suspended: host mta5.am0.yahoodns.net[98.138.112.37] refused to talk to me: 421 4.7.0 [TS01] Messages from 216.119.158.65 temporarily deferred due to user complaints - 4.16.55.1; see http://postmaster.yahoo.com/421-ts01.html)
(my-ip-was-here) 26 17:51:59 julia postfix/error[11570]: 2E47A8714B: to=<k8steveog0817@yahoo.com>, relay=none, delay=129357, delays=129356/0.07/0/1.2, dsn=4.7.0, status=deferred (delivery temporarily suspended: host mta5.am0.yahoodns.net[98.138.112.37] refused to talk to me: 421 4.7.0 [TS01] Messages from 216.119.158.65 temporarily deferred due to user complaints - 4.16.55.1; see http://postmaster.yahoo.com/421-ts01.html)
(my-ip-was-here) 26 17:51:59 julia postfix/error[11392]: 40C7416F5C5: to=<piju@mysite.org>, relay=none, delay=8020, delays=8020/0.14/0/0.05, dsn=5.0.0, status=bounced (User unknown in virtual alias table)
(my-ip-was-here) 26 17:51:59 julia postfix/qmgr[11330]: 1F25FB3D50: from=<myvet@mysite.org>, size=660, nrcpt=9 (queue active)
(my-ip-was-here) 26 17:51:59 julia postfix/smtp[11486]: 1D21866B04: host mta5.am0.yahoodns.net[63.250.192.45] refused to talk to me: 421 4.7.0 [TS01] Messages from 216.119.158.65 temporarily deferred due to user complaints - 4.16.55.1; see http://postmaster.yahoo.com/421-ts01.html

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(mysite.org) being where our domain name was.

So, two ways to lock down smtp relaying:  by IP/subnet and SMTP AUTH.  Are you doing one or both?

If by IP, a customer has to be infected.  If by auth, then someone's credentials are compromised (and are probably also infected).

If you go through your maillog for yesterday, you should be able to see a pattern of who is sending a lot of email or who is sending from multiple foreign addresses.

SMTP AUTH.

I do have one particular user sending mail - but I deleted that user account from the server, and still it's showing in the log that she's sending........  odd.

You need to stop Postfix, kill all the connections and restart it.

Ok, I did restart postfix, even rebooted the server, would that have killed all the connections or could something have persisted, seems like that would have killed it.

The hosting company is running a maldet scan on it now...

(and in the meantime, I'm setting up a new server)

I see compromised credentials get used to send spam on a regular basis.  It doesn't mean that your server is compromised (unless your accounts have shell access -- that can be a game changer), it just means that a user has a compromised machine.

If Postfix is like Sendmail in that any existing connections get pushed to PID 1 on a restart, then that won't do any good.  A reboot, on the other hand, will take care of any existing open channels.

Ok, thank you. They don't have shell access, just email. I don't even host any websites on the server, we just use it for email.

So after the reboot, that should have killed all connections, if I understand you correctly..

I'll let them finish the scan and see what that does, I don't want to try another reboot while they are running the scan, and I'm setting up a vps as a backup just in case they find something and I have to move users to another - hopefully leaving any issues behind.

Thank you, it has been great to have someone to staff this with a bit -

Chris

Thank you for the original answer and ongoing help!