Could not connect to socket /var/imap/socket/lmtp: Connection refused by localhost

[Eugene M. Zheganin]

Hi,

I'm using cyrus-imapd for quite long, but recently I encountered an
issue with delivery: one of my mail servers is handling a significant
load of e-mails, and quite often I'm seeing line like this in the maillog:

Jan 17 12:35:26 gw0 sm-mta[78888]: v0H7ZML4078586: SYSERR(root): Could
not connect to socket /var/imap/socket/lmtp: Connection refused by localhost

This usually means that message bounced to MTA queue, where it can be
hold for several minutes, sometimes dozens of minutes. I have the
following directive in the cyrus.conf:

SERVICES {
    ...
    lmtp cmd="lmtpd" listen="localhost:lmtp" prefork=4 maxchild=16
    lmtpunix cmd="lmtpd" listen="/var/imap/socket/lmtp" prefork=4
maxchild=16 maxfds=2048
}

I discovered that simply increasing this value can make the situation
even worse. Is there some decent aproach to increase the performance of
lmtp ?

Thanks.
Eugene.