qmail - 421 unable to read controls

Hello All,

I’m wondering if any of you interworx folk get this error when sending email.

Konto: ‘username@domainname.com’, Server: ‘mail.domainname.com’, Protokoll: SMTP, Serverantwort: ‘421 unable to read controls (#4.3.0)’, Port: 25, Secure (SSL): Nein, Serverfehler: 421, Fehlernummer: 0x800CCC67

(I know its in german but you can still get the error)

Information I have found on the net:
qmail-smtpd-auth-0.31 has a minor bug if you use morercpthosts. After a failed authentication attempt, if the client attempts to send mail to a domain which is not listed in rcpthosts, qmail-smtpd is unable to read morercpthosts.cdb. Instead, it sends “421 unable to read controls (#4.3.0)” and drops the connection. qmail-smtpd-auth-close3.patch fixes this bug by closing file descriptor 3 (only if necessary) in the authentication child process rather than the parent process.

Any ideas if this is the case? I have the latest version of interworx running on my server.
InterWorx-CP v2.1.3
qmail 1.03


I doubt it’s the auth bug you mention - if it were we would have seen it before. My guess without looking at the box is permissions on the qmail dirs and/or files. If you can’t figure it out you may want to open a support ticket.


Uhm if its permissions - then its constantly changing - Customer says it doesn’t happen often but periodically.

why would permissions change occasionally? Any solutions?

Permissions shouldn’t change occasionally. Were you able to track it down to permissions problem? Maybe it’s a memory limit problem. You could try increasing the /service/smtp/run file’s memory limit. It looks like

exec /usr/bin/softlimit -m SOME-NUMBER-HERE \

you could try doubling the SOME-NUMBER.

Is the problem easily reproducable or completely random? Random sounds like memory limit is a possiblity.