我的 Postfix 系统可以访问，一切正常（我昨天设置了它）。但今天有好几次都无法访问，我真的不知道该怎么办。通常当它无法工作时，它都是这样的：我尝试在计算机上登录 Mozilla Thunderbird 后在手机上登录我的邮件帐户。在我的手机上设置邮件帐户似乎不起作用。尝试在手机上登录后，服务器（IMAP 和 SMTP）根本没有响应。我尝试使用 telnet“联系”它，但没有成功。然后等了几分钟后，它就像什么都没发生一样工作了。有一点需要注意：来自服务器的连接（使用 roundcube）始终有效。
我就是搞不清楚这里发生了什么，是什么导致整个服务器没有响应（日志显示没有任何异常）。任何帮助都非常感谢 :)
我的main.cf如下：
smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
biff = no
# appending .domain is the MUA's job.
append_dot_mydomain = no
# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h
readme_directory = no
# See http://www.postfix.org/COMPATIBILITY_README.html -- default to 2 on
# fresh installs.
compatibility_level = 2
# TLS parameters
smtpd_tls_cert_file = /etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file = /etc/ssl/private/ssl-cert-snakeoil.key
smtpd_tls_security_level = may
smtp_tls_CApath=/etc/ssl/certs
smtp_tls_security_level = dane
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
myhostname = example.com
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
mydestination = $myhostname, , localhost
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_command = /usr/bin/procmail-wrapper -o -a $DOMAIN -d $LOGNAME
mailbox_size_limit = 0
recipient_delimiter = +
inet_protocols = all
virtual_alias_maps = hash:/etc/postfix/virtual
sender_bcc_maps = hash:/etc/postfix/bcc
sender_dependent_default_transport_maps = hash:/etc/postfix/dependent
home_mailbox = Maildir/
smtpd_sasl_auth_enable = yes
broken_sasl_auth_clients = yes
smtpd_recipient_restrictions = permit_mynetworks permit_sasl_authenticated reject_unauth_destination
smtp_dns_support_level = dnssec
smtp_host_lookup = dns
allow_percent_hack = no
tls_server_sni_maps = hash:/etc/postfix/sni_map
mynetworks_style = subnet