pam(foobar@example.com,192.0.1.1,<9zMTUUCGNfHZzMpL>): unknown user (SHA1 of given password: ff75068c2f4d700a49dae204d56477a5ffa5d23d)

The password is correct, i.e. 'echo -n 'passed' | openssl dgst -sha1' matches.

The user is setup correctly in /etc/dovecot/users (the /etc/dovecot/users was copied from another known-good server, so the syntax is correct and appropriate adjustments have been made for chmod and directory).

doveconf -N follows:

# 2.3.3 (dcead646b): /etc/dovecot/dovecot.conf # Pigeonhole version 0.5.3 (f018bbab) # OS: Linux 4.12.14-lp150.12.48-default x86_64 # Hostname: foobar auth_mechanisms = plain login auth_verbose = yes auth_verbose_passwords = sha1 doveadm_password = # hidden, use -P to show it first_valid_uid = 471 imapc_features = rfc822.size fetch-headers imapc_host = foobar.example.com imapc_password = # hidden, use -P to show it imapc_port = 993 imapc_ssl = imaps imapc_user = %u mail_location = maildir:~/Maildir mail_plugin_dir = /usr/lib64/dovecot/modules mail_prefetch_count = 20 mailbox_list_index = yes 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 environment mailbox date ihave enotify namespace inbox { inbox = yes location = mailbox Drafts { special_use = \Drafts } mailbox Junk { special_use = \Junk } mailbox Sent { special_use = \Sent } mailbox "Sent Messages" { special_use = \Sent } mailbox Trash { special_use = \Trash } prefix = } passdb { driver = pam name = } plugin { sieve = file:~/.dovecot.sieve } protocols = imap lmtp service auth { unix_listener /var/spool/postfix/private/dovecot-auth { group = postfix mode = 0660 user = postfix } } service imap-login { process_min_avail = 3 } service lmtp { process_min_avail = 5 unix_listener /var/spool/postfix/private/dovecot-lmtp { group = postfix mode = 0660 user = postfix } user = my_virtmailuser } service managesieve-login { inet_listener sieve { port = 4190 } inet_listener sieves { address = port = 5190 ssl = yes } } ssl = required ssl_ca = </etc/dovecot/ssl/certbot_ca.pem ssl_cert = </etc/dovecot/ssl/certbot.pem ssl_cipher_list = ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA:ECDHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-RSA-AES256-SHA256:DHE-RSA-AES256-SHA:ECDHE-ECDSA-DES-CBC3-SHA:ECDHE-RSA-DES-CBC3-SHA:EDH-RSA-DES-CBC3-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:DES-CBC3-SHA:!DSS ssl_client_ca_dir = /etc/ssl/certs ssl_dh = # hidden, use -P to show it ssl_key = # hidden, use -P to show it ssl_min_protocol = TLSv1.2 ssl_options = no_compression ssl_prefer_server_ciphers = yes userdb { driver = passwd name = } userdb { args = scheme=ARGON2ID username_format=%u /etc/dovecot/users auth_verbose = yes driver = passwd-file name = } protocol lmtp { mail_plugins = sieve postmaster_address = foobar@example.com } protocol lda { deliver_log_format = msgid=%m: %$ mail_plugins = sieve postmaster_address = postmaster quota_full_tempfail = yes rejection_reason = Your message to <%t> was automatically rejected:%n%r } protocol imap { mail_max_userip_connections = 20 }