Hello,

I migrated our mail infrastructure to Dovecot on Ubuntu 18.04 some months ago. It works fine, but recently some users told me that they sometime receive duplicated emails. Same email content, same headers including message-id.

I'm using two dovecot servers on two sites. Both server are in cluster. We don't use shared folders. All users that reported this issue so far are using the same server instance. The problematic emails are coming from local users on that instance too. The examples they given to me was emails with many recipients (To/CC). A specific message can be received twice (or more) by recipient A but only once by recipient B. I didn't see anything in the logs about sieve rules that redirect emails to others recipients.

Where should I look to diagnostic this issue?

Thanks.

Server config: # 2.2.33.2 (d6601f4ec): /etc/dovecot/dovecot.conf # Pigeonhole version 0.4.21 (92477967) doveconf: Warning: service auth { client_limit=1000 } is lower than required under max. load (2500) doveconf: Warning: service anvil { client_limit=1000 } is lower than required under max. load (1503) # OS: Linux 4.15.0-60-generic x86_64 Ubuntu 18.04.3 LTS auth_default_realm = **edited** auth_master_user_separator = * auth_mechanisms = plain login default_process_limit = 500 first_valid_uid = 200 last_valid_uid = 200 mail_location = mbox:~/mail:INBOX=/var/mail/%u mail_plugins = " notify replication zlib quota" mail_privileged_group = mail managesieve_notify_capability = mailto managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date index ihave duplicate mime foreverypart extracttext vnd.dovecot.debug mdbox_rotate_size = 10 M namespace inbox { inbox = yes location = mailbox "Éléments envoyés" { special_use = \Sent } mailbox "Éléments supprimés" { special_use = \Trash } mailbox Brouillon { special_use = \Drafts } mailbox "Courrier indésirable" { special_use = \Junk } mailbox Drafts { auto = subscribe special_use = \Drafts } mailbox Junk { auto = subscribe special_use = \Junk } mailbox Sent { auto = subscribe special_use = \Sent } mailbox "Sent Messages" { special_use = \Sent } mailbox Trash { auto = subscribe special_use = \Trash } prefix = INBOX/ separator = / } passdb { args = /etc/dovecot/dovecot-ldap.conf.ext driver = ldap } passdb { args = /etc/dovecot/passwd.masterusers driver = passwd-file master = yes } plugin { mail_replica = tcps:**edited**:53683 quota = count:User quota quota_grace = 10%% quota_rule = *:storage=10G quota_rule2 = INBOX/Trash:storage=+100M quota_status_nouser = DUNNO quota_status_overquota = 552 5.2.2 La boite courriel du destinataire est pleine - Mailbox is full quota_status_success = DUNNO quota_vsizes = yes quota_warning = storage=100%% quota-warning 100 %u quota_warning2 = storage=95%% quota-warning 95 %u quota_warning3 = storage=90%% quota-warning 90 %u quota_warning4 = storage=85%% quota-warning 85 %u quota_warning5 = storage=75%% quota-warning 75 %u quota_warning6 = -storage=80%% quota-warning '-80' %u quota_warning7 = -storage=100%% quota-warning '-100' %u sieve = /var/vmail/domains/%Ld/%Ln/.dovecot.sieve sieve_before = /var/vmail/sieve/before.sieve sieve_default = /var/vmail/sieve/default.sieve sieve_extensions = +vnd.dovecot.debug sieve_global = /var/vmail/sieve/global zlib_save = lz4 } protocols = " imap lmtp sieve" service auth { unix_listener /var/spool/postfix/private/auth { mode = 0666 } unix_listener auth-userdb { group = vmail mode = 0666 user = vmail } } service imap-login { inet_listener imap { port = 0 } process_min_avail = 10 } service lmtp { unix_listener /var/spool/postfix/private/dovecot-lmtp { group = postfix mode = 0660 user = postfix } } service quota-status { client_limit = 1 executable = quota-status -p postfix inet_listener { address = **edited** port = 53684 } } service quota-warning { executable = script /usr/local/bin/quota-warning.sh unix_listener quota-warning { user = vmail } } ssl = required ssl_cert = **edited**/**edited**.crtbundle ssl_client_ca_dir = /etc/ssl/certs ssl_key = # hidden, use -P to show it userdb { args = /etc/dovecot/dovecot-ldap.conf.ext driver = ldap } protocol lmtp { mail_plugins = " notify replication zlib quota sieve" postmaster_address = postmaster@**edited** } protocol imap { mail_plugins = " notify replication zlib quota imap_zlib imap_quota" }

-- Francis