I?ve installed and configured Apple?s calendar server. It seems to be working just fine. However it keeps trying to speak to my IMAP server ? don?t know why ? and the authentication attempts fail every 30 seconds or so. Here?s what?s in the calendar server logs: 2016-01-07 22:42:38+0000 [-] [caldav-1] [IMAP4DownloadProtocol (TLSMemoryBIOProtocol),client] [txdav.caldav.datastore.scheduling.imip.inbound.IMAP4DownloadProtocol#error] IMAP login failed for com.apple.calendarserver 2016-01-07 22:43:08+0000 [-] [caldav-1] [IMAP4DownloadProtocol (TLSMemoryBIOProtocol),client] [txdav.caldav.datastore.scheduling.imip.inbound.IMAP4DownloadProtocol#error] IMAP login failed for com.apple.calendarserver 2016-01-07 22:43:39+0000 [-] [caldav-1] [IMAP4DownloadProtocol (TLSMemoryBIOProtocol),client] [txdav.caldav.datastore.scheduling.imip.inbound.IMAP4DownloadProtocol#error] IMAP login failed for com.apple.calendarserver And in dovecot?s logs I see: Jan 7 22:47:43 hutch dovecot[63067]: imap-login: Disconnected (auth failed, 2 attempts in 4 secs): user=<com.apple.calendarserver>, method=PLAIN, rip=195.54.233.70, lip=195.54.233.70, TLS, session=<wkMAQsYoVADDNulG> Jan 7 22:48:10 hutch dovecot[63067]: auth-worker(65378): Error: pam(com.apple.calendarserver,195.54.233.70): pam_acct_mgmt() failed: permission denied Jan 7 22:48:14 --- last message repeated 1 time --- Jan 7 22:48:14 hutch dovecot[63067]: imap-login: Disconnected (auth failed, 2 attempts in 4 secs): user=<com.apple.calendarserver>, method=PLAIN, rip=195.54.233.70, lip=195.54.233.70, TLS, session=<dSvTQ8YoXQDDNulG> Jan 7 22:48:40 hutch dovecot[63067]: auth-worker(65378): Error: pam(com.apple.calendarserver,195.54.233.70): pam_acct_mgmt() failed: permission denied Jan 7 22:48:44 --- last message repeated 1 time ? I tweaked dovecot to use AUTH PLAIN as well as CRAM-MD5. [The MD5 stuff has always worked fine for SMTP and IMAP over TLS.] I think /etc/pam.d/dovecot is OK too: % cat /etc/pam.d/dovecot # # as documented on Dovecot wiki auth required pam_opendirectory.so try_first_pass account required pam_nologin.so account required pam_opendirectory.so password required pam_opendirectory.so Here?s my dovecot.conf: # 2.2.5: dovecot.conf # OS: Darwin 12.5.0 x86_64 auth_mechanisms = plain login cram-md5 base_dir = /var/run/dovecot/ listen = *, [::] mail_debug = yes mail_privileged_group = mail mbox_write_locks = fcntl namespace inbox { hidden = yes inbox = yes list = no location = mbox:~/mail:INBOX=/var/mail/%u prefix = "#mbox/" separator = / type = private } namespace { inbox = no list = yes location = maildir:/var/imap/%u:LAYOUT=fs prefix = separator = / type = private } passdb { driver = pam args = failure_show_msg=yes } passdb { args = /usr/local/etc/dovecot-md5 driver = passwd-file } protocols = imap service auth { executable = /usr/local/libexec/dovecot/auth unix_listener /var/spool/postfix/private/auth { group = postfix mode = 0660 user = postfix } user = root } service imap-login { client_limit = 32 executable = /usr/local/libexec/dovecot/imap-login inet_listener imap { port = 0 } process_limit = 128 process_min_avail = 3 service_count = 1 vsz_limit = 64 M } service imap { executable = /usr/local/libexec/dovecot/imap process_limit = 32 } service pop3-login { client_limit = 32 process_limit = 128 process_min_avail = 3 service_count = 1 vsz_limit = 64 M } service pop3 { process_limit = 32 } ssl_cert = </usr/local/etc/ssl/certs/dovecot.pem ssl_cipher_list = ALL:!LOW:!SSLv2 ssl_key = </usr/local/etc/ssl/private/dovecot.pem syslog_facility = local4 userdb { driver = passwd } protocol imap { mail_max_userip_connections = 10 mail_plugin_dir = /usr/local/lib/dovecot/imap } protocol lda { postmaster_address = postmaster at example.com } Can someone please explain what?s going on and how to fix/troubleshoot it? Thanks. The endless error messages in the log don?t seem to be causing any problems to either the mail setup or the calendaer server. Famous last words? However they are a bit annoying and probably point to an underlying problem or misconfiguration that really should be fixed. By the way, the password used by the calendar server is for my MacOSX login (which should be getting picked up via PAM, right?) while a different one is used for the SMTP/IMAP MD5 challenge-response. I hope someone can clear up my confusion.