Sep 22
dovecot: master: Warning: service(imap-login): process_limit (256) reached, client connections are being dropped

So you found this error message in your server logs and noticed you cannot login anymore via IMAP because all available ‘slots’ have been consumed. My working theory is, it is related to the IOS7 release and it’s IPv6 support.  With privacy extensions enabled ( See RFC 4941 ) it looks like the IOS device is grabbing a new IPv6 address every time it wakes up. This is a perfect fine behaviour if it weren’t for IMAP IDLE. From my understanding, IMAP idle is sort of a long lasting SSL tunnel with a very long TTL. This way your client doesn’t need to be online all the time and only wakes up, if there anything new on the server ( RFC 2177 ).

Workaround: Break IMAP IDLE. Not really, but at least reduce the TTL for the Tunnel by somewhat. Don’t be to harsh, otherwise your’e mobile device is gonna wake up too often, therefore consuming too much power. I set it to 30minutes.

protocol imap {
 #process_limit = 512
 # process_min_avail = 5
 imap_idle_notify_interval = 30 mins
 mail_max_userip_connections = 10
}
#You can check your configuration by using "doveconf -N" before reloading/restarting.

If it works, dovecot will drop the connections to not responsive ‘expired’ IPv6 IPs, freeing resources.

Sep 22 11:04:36 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=273/1229
Sep 22 11:04:37 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=237/1161
Sep 22 11:04:37 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=189/1073
Sep 22 11:04:37 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=222/1132
Sep 22 11:04:37 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=294/1268
Sep 22 11:04:37 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=273/1229
Sep 22 11:04:37 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=222/1211
Sep 22 11:04:40 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=246/1180
Sep 22 11:04:40 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=288/1258
Sep 22 11:04:40 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=252/1190
Sep 22 11:04:40 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=273/1229
Sep 22 11:04:40 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=267/1219
Sep 22 11:04:40 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=288/1258
Sep 22 11:04:40 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=252/1190
Sep 22 11:04:40 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=165/1104
Sep 22 11:04:40 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=210/1112
Sep 22 11:04:40 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=216/1201
Sep 22 11:04:40 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=237/1161
Sep 22 11:04:40 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=189/1073
Sep 22 11:04:40 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=237/1161
Sep 22 11:04:40 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=273/1229
Sep 22 11:04:41 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=216/1122
Sep 22 11:04:41 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=258/1200
Sep 22 11:04:41 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=201/1172
Sep 22 11:04:41 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=252/1190
Sep 22 11:04:41 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=231/1151
Sep 22 11:04:41 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=231/1151
Sep 22 11:04:41 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=252/1190
Sep 22 11:04:41 mx dovecot: imap(email@server): Disconnected: Disconnected in IDLE bytes=189/1073
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