Here are the logs from the IMAP (last group of timestamps). Are there any other logs that would be useful?
IMAP
Mar 8 10:56:27 server dovecot[38993]: IMAP(*): Master disconnected (pid 39117)
Mar 8 10:56:27 server dovecot[38993]: IMAP(*): Master disconnected (pid 39070)
Mar 8 10:58:51 server dovecot[39343]: imap-login: Login: user=<dean>, method=PLAIN, rip=76.21.19.69, lip=192.168.1.210, TLS
Mar 8 10:58:51 server dovecot[39343]: IMAP(*): maildir: data=/Volumes/External HD3/spool/imap/dovecot/mail/F037805C-94D5-47B8-8D48-DC15F14905AC
Mar 8 10:58:51 server dovecot[39343]: IMAP(*): maildir++: root=/Volumes/External HD3/spool/imap/dovecot/mail/F037805C-94D5-47B8-8D48-DC15F14905AC, index=, control=, inbox=/Volumes/External HD3/spool/imap/dovecot/mail/F037805C-94D5-47B8-8D48-DC15F14905AC
Mar 8 10:58:51 server dovecot[39343]: imap-login: Login: user=<dean>, method=PLAIN, rip=76.21.19.69, lip=192.168.1.210, TLS
Mar 8 10:58:51 server dovecot[39343]: IMAP(*): maildir: data=/Volumes/External HD3/spool/imap/dovecot/mail/F037805C-94D5-47B8-8D48-DC15F14905AC
Mar 8 10:58:51 server dovecot[39343]: IMAP(*): maildir++: root=/Volumes/External HD3/spool/imap/dovecot/mail/F037805C-94D5-47B8-8D48-DC15F14905AC, index=, control=, inbox=/Volumes/External HD3/spool/imap/dovecot/mail/F037805C-94D5-47B8-8D48-DC15F14905AC
Mar 8 11:00:51 server dovecot[39343]: imap-login: Login: user=<dean>, method=PLAIN, rip=76.21.19.69, lip=192.168.1.210, TLS
Mar 8 11:00:51 server dovecot[39343]: IMAP(*): maildir: data=/Volumes/External HD3/spool/imap/dovecot/mail/F037805C-94D5-47B8-8D48-DC15F14905AC
Mar 8 11:00:51 server dovecot[39343]: IMAP(*): maildir++: root=/Volumes/External HD3/spool/imap/dovecot/mail/F037805C-94D5-47B8-8D48-DC15F14905AC, index=, control=, inbox=/Volumes/External HD3/spool/imap/dovecot/mail/F037805C-94D5-47B8-8D48-DC15F14905AC
Mar 8 11:02:28 server dovecot[39343]: imap-login: Login: user=<dean>, method=CRAM-MD5, rip=192.168.1.210, lip=192.168.1.210, TLS
Mar 8 11:02:28 server dovecot[39343]: IMAP(*): maildir: data=/Volumes/External HD3/spool/imap/dovecot/mail/F037805C-94D5-47B8-8D48-DC15F14905AC
Mar 8 11:02:28 server dovecot[39343]: IMAP(*): maildir++: root=/Volumes/External HD3/spool/imap/dovecot/mail/F037805C-94D5-47B8-8D48-DC15F14905AC, index=, control=, inbox=/Volumes/External HD3/spool/imap/dovecot/mail/F037805C-94D5-47B8-8D48-DC15F14905AC