我一直在尝试使用 postfix 设置邮件服务器。可以发送/接收本地邮件并接收外部邮件。但是，发送外部邮件不起作用。
当我开始通过telnet example.com 25输入后我收到以下消息收件地址：[电子邮件保护]：
454 4.7.1 <[电子邮件保护]>：中继访问被拒绝
一些可能有用的信息：
/etc/postfix/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 = example.com
virtual_alias_maps = hash:/etc/postfix/virtual
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
mydestination = example.com, mycomputername, localhost.localdomain, localhost
relayhost = mail.example.com
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128 192.168.0.0/24
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
inet_protocols = all
答案1
事实证明，我的互联网服务提供商 (ISP) 阻止了外发邮件。但他们提供了一个中继选项：smtp.myisp.tld。我必须在 /etc/postfix/main.cf 配置文件中使用此地址作为我的中继主机：
relayhost = smtp.myisp.tld