I assume you are refering to incomming mail. I had sometimes similar issues with mbox and having sendmail deliver straight to the mbox file. When I switched to delivering to lmtp, I never encountered it anymore. Just put this lmtp inbetween.
> -----Original Message----- > From: dovecot <dovecot-boun...@dovecot.org> On Behalf Of gmail > Sent: 14 March 2021 23:30 > To: dovecot@dovecot.org > Subject: Re: Latest dovecot does not work with latest MUA (thunderbird) > > > Stuart Henderson kirjoitti 14.3.2021 klo 23.38: > > On 2021-03-14, lja@koti <l...@lja.fi> wrote: > >> # 2.3.7.2 (3c910f64b): /etc/dovecot/dovecot.conf > > That's nowhere near the latest Dovecot. > > > > > Updated dovecot to bleeding edge, and still got same issue. > > # 2.4.devel (b0f498b69): /usr/local/etc/dovecot/dovecot.conf > # OS: Linux 5.9.0-rc5 x86_64 Ubuntu 20.04.2 LTS > # Hostname: superman.sillywalk.org > auth_debug = yes > auth_debug_passwords = yes > auth_mechanisms = plain login > auth_verbose = yes > auth_verbose_passwords = plain > debug_log_path = /var/log/dovecot-debug.log > info_log_path = /var/log/dovecot-info.log > log_path = /var/log/dovecot.log > mail_debug = yes > mail_location = maildir:~/Maildir/ > mbox_write_locks = fcntl > 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 > } > protocols = imap pop3 > service auth { > unix_listener /var/spool/postfix/private/auth { > group = mail > mode = 0660 > user = postfix > } > } > ssl_cert = </etc/letsencrypt/live/maindomain.fi/fullchain.pem > ssl_key = # hidden, use -P to show it > userdb { > driver = passwd > } > protocol imap { > imap_metadata = yes > } > local_name businessdomain.fi { > ssl_cert = </etc/letsencrypt/live/businessdomain.fi/fullchain.pem > ssl_key = # hidden, use -P to show it > } > local_name businessdomain.com { > ssl_cert = </etc/letsencrypt/live/businessdomain.com/fullchain.pem > ssl_key = # hidden, use -P to show it > } > local_name maindomain.fi { > ssl_cert = </etc/letsencrypt/live/maindomain.fi/fullchain.pem > ssl_key = # hidden, use -P to show it > }