我刚刚用默认设置设置了 postfix（使用 taskel install mail-server）。不幸的是，我无法通过 SMTP 服务器发送电子邮件。
这是我的main.cf：
# See /usr/share/postfix/main.cf.dist for a commented, more complete version
# Debian specific: Specifying a file name will cause the first
# line of that file to be used as the name. The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname
smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no
# appending .domain is the MUA's job.
append_dot_mydomain = no
# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h
readme_directory = no
# TLS parameters
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.
smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
myhostname = mydomain.tld
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
mydestination = mydomain.tld, PC-01, localhost.localdomain, localhost
relayhost =
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_command = procmail -a "$EXTENSION"
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
inet_protocols = all
其中 mydomain.tld 是我的域名（惊喜，惊喜……）。
我已经检查过 /var/log/mail.log 并且它一直显示：
Jun 16 20:38:59 PC-01 postfix/smtp[12967]: connect to mta5.am0.yahoodns.net[66.196.118.37]:25: Connection timed out
我也花了一晚上的时间在 Google 上搜索这个问题，其他人说这可能是由 ISP 引起的，因为他们阻止了端口 25。我在网上查过了，但我认为不是。（我该如何确定？）
如果你能帮助我，我将非常感激。
答案1
您是否收到来自远程邮件服务器的 SMTP 问候消息？
telnet 66.196.118.37 25
您可以使用 tcptraceroute 来定位阻止 SMTP 连接的防火墙。