[Dovecot] unable to lock for exclusive access: Resource temporarily unavailable

Dears,

We have a mail server (RHEL 6.0, Postfix and Dovecot 1.0.7).

The output of dovecot -n is the following:

# 1.0.7: /etc/dovecot.conf

protocols: pop3

login_dir: /var/run/dovecot/login

login_executable: /usr/libexec/dovecot/pop3-login

mail_location: mbox:~/mail:INBOX=/var/mail/%u

mail_executable: /usr/libexec/dovecot/pop3

mail_plugin_dir: /usr/lib/dovecot/pop3

pop3_client_workarounds: outlook-no-nuls oe-ns-eoh

auth default:

passdb:

driver: pam

userdb:

driver: passwd

During the last days we face the following problem:

There is great delay in the delivery of the emails. Some seem to not be delivered at all. Issuing the mailq command we get the following message for almost all the email accounts:

(cannot update mailbox /var/mail/xyz for user xyz. unable to lock for exclusive access: Resource temporarily unavailable)

Please send to me any suggestions, because I cannot resolve it and I receive a lot of pressure.

Best Regards,

Nikos