我有一个带有 postfix 和 dovecot 的邮件服务器，我可以用它在自己的电子邮件地址接收邮件。
当我通过 POP3 从远程邮件客户端连接时，即使我提供了正确的密码，它也会说身份验证失败。
但邮件客户端仍然能够在没有适当身份验证的情况下从我的帐户发送邮件。
我该如何配置它以便需要身份验证才能发送电子邮件？
postconf -n 的输出为 -
alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
append_dot_mydomain = no
biff = no
broken_sasl_auth_clients = yes
config_directory = /etc/postfix
home_mailbox = Maildir/
inet_interfaces = all
inet_protocols = all
mailbox_command =
mailbox_size_limit = 0
mydestination = example.com, mail.example.com, localhost.example.com, localhost
myhostname = mail.example.com
mynetworks = 127.0.0.0/8
myorigin = /etc/mailname
readme_directory = no
recipient_delimiter = +
relayhost =
smtp_tls_note_starttls_offer = yes
smtp_tls_security_level = may
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
smtpd_recipient_restrictions = permit_sasl_authenticated,permit_mynetworks,reject_unauth_destination
smtpd_sasl_auth_enable = yes
smtpd_sasl_local_domain =
smtpd_sasl_security_options = noanonymous
smtpd_sasl_type = cyrus
smtpd_sender_restrictions = reject_unknown_sender_domain, reject_unknown_recipient_domain, reject_unauth_pipelining
smtpd_tls_CAfile = /etc/ssl/certs/cacert.pem
smtpd_tls_auth_only = no
smtpd_tls_cert_file = /etc/ssl/certs/smtpd.crt
smtpd_tls_key_file = /etc/ssl/private/smtpd.key
smtpd_tls_loglevel = 1
smtpd_tls_mandatory_ciphers = medium
smtpd_tls_mandatory_protocols = SSLv3, TLSv1
smtpd_tls_received_header = yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtpd_tls_session_cache_timeout = 3600s
tls_random_source = dev:/dev/urandom
谢谢