为了在我的 Postfix 服务器上使用 TLS，我直接使用了来自其他服务器的 nginx ssl 文件，该服务器也使用了我想要与 postfix 一起使用的域。
我按照下面的方式将文件集成到main.cf中：
smtpd_tls_cert_file = /etc/ssl/subdomain.example.com.crt
smtpd_tls_key_file = /etc/ssl/subdomain.example.com.key
smtpd_tls_CAfile = /etc/ssl/subdomain.example.com.pem
我没有对 openssl 或类似的东西进行任何操作，我只是在 nginx 中使用了用于另一台服务器的文件。但我想这应该不是问题，因为邮件服务器也使用与 nginx 相同的域。
通过 shell () 使用 postfix 发送邮件mail完全没有问题，但是当我想使用我的 postfix 服务器作为中继服务器时，出现以下错误（场景：我想在 PHP-CMS 中使用我的 smtp 服务器）：
cannot enable STARTTLS, though 'subdomain.example.com:25' advertised it:
4.7.0 TLS not available due to local problem (454)
邮件日志：
Feb 5 15:40:09 koto postfix/smtpd[8911]: warning: TLS library problem: error:2006D080:BIO routines:BIO_new_file:no such file:bss_file.c:172:
Feb 5 15:40:09 koto postfix/smtpd[8911]: warning: TLS library problem: error:0B084002:x509 certificate routines:X509_load_cert_crl_file:system lib:by_file.c:274:
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_tls_cert_file = /etc/ssl/subdomain.example.com.crt
smtpd_tls_key_file = /etc/ssl/subdomain.example.com.key
smtpd_tls_CAfile = /etc/ssl/subdomain.example.com.pem
smtpd_tls_auth_only = yes
smtpd_tls_session_cache_timeout = 3600s
smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
biff = no
# appending .domain is the MUA's job.
append_dot_mydomain = no
# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h
readme_directory = no
# TLS parameters
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.
smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
myhostname = debian-512mb-fra1-01
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
mydestination = **domain**, debian-512mb-fra1-01, localhost.localdomain, localhost
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_command = procmail -a "$EXTENSION"
recipient_delimiter = +
inet_interfaces = all
inet_protocols = all
mime_header_checks = regexp:/etc/postfix/header_checks
header_checks = regexp:/etc/postfix/header_checks
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = *****
smtp_sasl_security_options = noanonymous
smtp_tls_security_level = encrypt
header_size_limit = 4096000
relayhost = [smtp.sendgrid.net]:587
==> 这里有什么问题？