This is the default Debian 12 Bookworm configuration for Dovecot 2.3:

default_process_limit = 100
default_client_limit = 1000
service imap-login {
  client_limit = 0
  process_limit = 0
  process_min_avail = 0
  service_count = 1
}

After increasing the default_process_limit = 400 you can still face the following warning log message:

dovecot: master: Warning: service(imap-login): process_limit (400) reached,
    client connections are being dropped

This is because the service_count = 1 limits each imap-login process to handle only one login request. This configuration is very high in security, but very inefficient.

Removing the limit with service_count = 0 you can set some limits specifically for the imap-login:

service imap-login {
    # 16 processi × 500 client = 8000
    service_count = 0
    process_min_avail = 8
    process_limit = 16
    client_limit = 500
}

With process_min_avail you can set how many processes are always ready to answer login requests, the process_limit is set to the number of available CPUs.

Mostra la configurazione di Docevot, solo i parametri diversi dal default:

doveconf -n

Alcune statistiche di funzionamento dei vari servizi:

doveadm service status imap
doveadm service status imap-login
doveadm who