我已经搜索了每个论坛、每篇文章、每个 serverfault.com 帖子以查找此问题。我正在使用全新的 Postfix 设置。它由 Virtualmin 管理。每当我尝试通过 TLS 发送邮件时，都会收到错误消息（已删除可识别信息）：
Sep 7 21:58:37 mail postfix/smtp[220916]: initializing the client-side TLS engine
Sep 7 21:58:37 mail postfix/tlsmgr[220917]: open smtpd TLS cache btree:/var/lib/postfix/smtpd_scache
Sep 7 21:58:38 mail postfix/tlsmgr[220917]: open smtp TLS cache btree:/var/lib/postfix/smtp_scache
Sep 7 21:58:38 mail postfix/tlsmgr[220917]: tlsmgr_cache_run_event: start TLS smtpd session cache cleanup
Sep 7 21:58:38 mail postfix/tlsmgr[220917]: tlsmgr_cache_run_event: start TLS smtp session cache cleanup
Sep 7 21:58:38 mail postfix/smtp[220918]: initializing the client-side TLS engine
Sep 7 21:58:38 mail postfix/smtp[220918]: 536A837552: TLS is required, but was not offered by host gmail-smtp-in.l.google.com[173.194.219.27]
Sep 7 21:58:38 mail postfix/smtp[220916]: E9C5637920: to=<test@TestSender.CheckTLS.com>, relay=ts11-do.checktls.com[165.227.190.238]:25, delay=3768, delays=3768/0.67/0.11/0, dsn=4.7.4, status=deferred (TLS is required, but was not offered by host ts11-do.checktls.com[165.227.190.238])
Sep 7 21:58:38 mail postfix/smtp[220918]: 536A837552: TLS is required, but was not offered by host alt1.gmail-smtp-in.l.google.com[172.217.197.27]
Sep 7 21:58:38 mail postfix/smtp[220918]: 536A837552: TLS is required, but was not offered by host alt2.gmail-smtp-in.l.google.com[108.177.12.27]
Sep 7 21:58:39 mail postfix/smtp[220918]: 536A837552: TLS is required, but was not offered by host alt3.gmail-smtp-in.l.google.com[64.233.186.27]
Sep 7 21:58:39 mail postfix/smtp[220918]: 536A837552: to=<myemail@gmail.com>, relay=alt4.gmail-smtp-in.l.google.com[209.85.202.27]:25, delay=3819, delays=3817/0.67/1.2/0, dsn=4.7.4, status=deferred (TLS is required, but was not offered by host alt4.gmail-smtp-in.l.google.com[209.85.202.27])
Sep 7 22:00:01 mail postfix/pickup[220911]: A9D8537D1D: uid=33 from=<www-data>
Sep 7 22:00:01 mail postfix/cleanup[221006]: A9D8537D1D: message-id=<20210908020001.A9D8537D1D@mail.mydomain.com>
我正在为我的证书使用letsencrypt（使用Virtualmin提取）。它将证书放在 /home/user/ssl。* 这是我的 main.cf（域替换为 example.com）：
alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
allow_percent_hack = no
append_dot_mydomain = no
biff = no
broken_sasl_auth_clients = yes
home_mailbox = Maildir/
inet_protocols = ipv4
mailbox_command = /usr/bin/procmail-wrapper -o -a $DOMAIN -d $LOGNAME
mailbox_size_limit = 0
milter_default_action = accept
mydomain = EXAMPLE.com
myhostname = mail.EXAMPLE.com
mynetworks_style = subnet
non_smtpd_milters = inet:localhost:8891
recipient_delimiter = +
sender_bcc_maps = hash:/etc/postfix/bcc
sender_dependent_default_transport_maps = hash:/etc/postfix/dependent
smtp_dns_support_level = dnssec
smtp_host_lookup = dns
smtp_tls_ciphers = high
smtp_tls_exclude_ciphers = MD5, DES, ADH, RC4, PSD, SRP, 3DES, eNULL, aNULL
smtp_tls_loglevel = 4
smtp_tls_mandatory_ciphers = high
smtp_tls_mandatory_exclude_ciphers = MD5, DES, ADH, RC4, PSD, SRP, 3DES, eNULL, aNULL
smtp_tls_mandatory_protocols = TLSv1.3,TLSv1.2,TLSv1.1,!TLSv1,!SSLv2,!SSLv3
smtp_tls_note_starttls_offer = yes
smtp_tls_protocols = TLSv1.3, TLSv1.2, TLSv1.1, !TLSv1, !SSLv2, !SSLv3
smtp_tls_security_level = encrypt
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtpd_milters = inet:localhost:8891
smtpd_recipient_restrictions = permit_mynetworks permit_sasl_authenticated reject_unauth_destination check_policy_service inet:127.0.0.1:10023
smtpd_relay_restrictions = ${{$compatibility_level} < {1} ? {} : {permit_mynetworks permit_sasl_authenticated defer_unauth_destination}}
smtpd_sasl_auth_enable = yes
smtpd_tls_ask_ccert = yes
smtpd_tls_cert_file=/home/EXAMPLE/ssl.cert
smtpd_tls_ciphers = high
smtpd_tls_exclude_ciphers = MD5, DES, ADH, RC4, PSD, SRP, 3DES, eNULL, aNULL
smtpd_tls_key_file=/home/EXAMPLE/ssl.key
smtpd_tls_loglevel = 4
smtpd_tls_mandatory_ciphers = high
smtpd_tls_mandatory_exclude_ciphers = MD5, DES, ADH, RC4, PSD, SRP, 3DES, eNULL, aNULL
smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3, !TLSv1, TLSv1.1, TLSv1.2, TLSv1.3
smtpd_tls_protocols = TLSv1.3, TLSv1.2, TLSv1.1, !TLSv1, !SSLv2, !SSLv3
smtpd_tls_received_header = yes
smtpd_tls_security_level = encrypt
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
tls_preempt_cipherlist = yes
tls_random_source = dev:/dev/urandom
tls_server_sni_maps = hash:/etc/postfix/sni_map
virtual_alias_maps = hash:/etc/postfix/virtual
virtual_alias_domains = $mydomain
我知道 ENCRYPT 强制 TLS - 使用 MAY 回退到非 TLS 连接，这是为了测试
这是我的master.cf
smtp inet n - n - - smtpd
pickup unix n - n 60 1 pickup
cleanup unix n - n - 0 cleanup
qmgr unix n - n 300 1 qmgr
#qmgr unix n - n 300 1 oqmgr
tlsmgr unix - - n 1000? 1 tlsmgr
rewrite unix - - n - - trivial-rewrite
bounce unix - - n - 0 bounce
defer unix - - n - 0 bounce
trace unix - - n - 0 bounce
verify unix - - n - 1 verify
flush unix n - n 1000? 0 flush
proxymap unix - - n - - proxymap
proxywrite unix - - n - 1 proxymap
smtp unix - - n - - smtp
relay unix - - n - - smtp
-o syslog_name=postfix/$service_name
# -o smtp_helo_timeout=5 -o smtp_connect_timeout=5
showq unix n - n - - showq
error unix - - n - - error
retry unix - - n - - error
discard unix - - n - - discard
local unix - n n - - local
virtual unix - n n - - virtual
lmtp unix - - n - - lmtp
anvil unix - - n - 1 anvil
scache unix - - n - 1 scache
postlog unix-dgram n - n - 1 postlogd
*** 我将配置恢复为默认值，希望有所帮助，但没有改变。
当我远程登录到我的服务器时，我得到了 starttls 的选项：
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
220 mail.EXAMPLE.com ESMTP Postfix
EHLO example.com
250-mail.EXAMPLE.com
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-8BITMIME
250-DSN
250 CHUNKING
我正在为我的防火墙使用 opnsense。我认为它不会通过 SMTP 检查阻止 TLS。
将设置设置为 MAY 而不是 ENCRYPT，我可以很好地发送和接收电子邮件。将其设置为 MAY，Google 和 checktls.com 报告说 TLS 没有被使用。
dmarc、spf 等的所有测试都恢复正常。这是在 Ubuntu 服务器 20 上运行的后缀（最新）。
我的环境：
- 数据中心中的托管服务器（对它们没有限制）
- Proxmox，截至 21 年 9 月 8 日是最新的
- 容器在 LXC、Ubuntu 20 中运行
- 容器位于 OPNSense 防火墙后面
- 基于 Web 的测试显示服务器提供 starttls
- 从服务器运行 telnet > 另一台服务器确实显示 starttls 作为选项
非常感谢任何帮助，谢谢。