We are seeing a few (0-15) proxy failures like the following out of ~3m successful proxied connections a day. Average session creation load over our peak hour is about 47/sec. The backend servers aren't logging anything that would suggest any internal problem like insufficient processes to handle the load. It doesn't seem to happen when utilization is lowest at night.

dovecot: imap-login: Error: proxy(foo): connect(1.1.1.1, 143) failed: Connection timed out (after 63 secs)

I'm curious if anyone else has seen any similar problems or has any suggestions.

# dovecot -n # 2.1.9: /etc/dovecot/dovecot.conf # OS: Linux 2.6.32-279.5.2.el6.x86_64 x86_64 Scientific Linux release 6.3 (Carbon) auth_master_user_separator = * auth_username_format = %Ln auth_verbose = yes auth_verbose_passwords = sha1 auth_worker_max_count = 64 mail_fsync = always mail_log_prefix = "%s(%u): session=%{session} " mail_plugins = stats zlib maildir_very_dirty_syncs = yes mmap_disable = yes passdb { args = /etc/dovecot/master-users driver = passwd-file master = yes } passdb { args = imap driver = pam } plugin { lazy_expunge = DELETED_MESSAGES. stats_refresh = 30 secs stats_track_cmds = yes } protocols = imap pop3 service anvil { client_limit = 10000 } service auth { client_limit = 10000 vsz_limit = 512 M } service doveadm { inet_listener { port = 1842 } unix_listener doveadm-server { mode = 0666 } } service imap-login { inet_listener imap { port = 143 } inet_listener imaps { port = 993 ssl = yes } process_limit = 7000 process_min_avail = 32 } service imap-postlogin { executable = script-login -d /etc/dovecot/bin/sonic-imap-postlogin user = $default_internal_user } service imap { executable = imap imap-postlogin process_limit = 4096 vsz_limit = 512 M } service pop3-login { inet_listener pop3 { port = 110 } inet_listener pop3s { port = 995 ssl = yes } process_limit = 2000 process_min_avail = 32 } service pop3-postlogin { executable = script-login -d /etc/dovecot/bin/sonic-pop3-postlogin user = $default_internal_user } service pop3 { executable = pop3 pop3-postlogin process_limit = 4096 } service stats { fifo_listener stats-mail { mode = 0666 } } shutdown_clients = no ssl = required ssl_ca =