This is a bit off-topic since it involves the official Apple calendar server. Sorry. I bought OSX Server, started the calendar service and have got calendar data imported to the server and visible to client apps. So far, so good. However, my logs are filling up with authentication failures and I don't have a clue what is wrong or why these are happening. It's not clear why the calendarserver is trying to speak to my dovecot IMAP server. Does anyone know what's wrong or how to troubleshoot and fix this? Every ~30 seconds, calendarserver reports: % tail /Library/Server/Calendar and Contacts/Logs/error.log 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 the dovecot logs, I get this: Jan 7 22:43:14 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 22:43:40 hutch dovecot[63067]: auth-worker(65378): Error: \ pam(com.apple.calendarserver,195.54.233.70): pam_acct_mgmt() failed: permission denied Jan 7 22:43:44 --- last message repeated 1 time --- an 7 22:43:44 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=<VBuoRcYocgDDNulG> Jan 7 22:44:11 hutch dovecot[63067]: auth-worker(65378): Error: pam(com.apple.calendarserver,145.54.233.70): pam_acct_mgmt() failed: permission denied Jan 7 22:44:19 --- last message repeated 1 time --- The dovecot server is configured to use PLAIN authentication with PAM and CRAM-MD5, both over TLS. The calendar server is using the credentials for my MacOS login. Which is presumably accessible via PAM for dovecot's imap-login. Mail accounts use MD5 challenge response (again over TLS) for SMTP and IMAPS logins. However my mail MD5 "password" is not the same as my MacOS password even though the user name is unchanged. I suppose the two passwords could be aligned, but I'd prefer to keep these separated. I'd be grateful for any advice and suggestions, thanks.