配置Postfix+Dovecot+MySQL邮件服务器后TLS连接失败，出现SSL_accept()版本号错误

嗨，我今天跟着教程配置了Postfix、Dovecot和MySQL邮件服务器，现在遇到了TLS连接的问题，想请大家帮忙看看。

我的服务器配置信息 #

Dovecot 配置（执行 dovecot -n 输出） #

# 2.3.16 (7e2e900c1a): /etc/dovecot/dovecot.conf
# Pigeonhole version 0.5.16 (09c29328)
# OS: Linux 5.15.0-92-generic x86_64 Ubuntu 22.04.3 LTS ext4
# Hostname: cermofi-lab

auth_mechanisms = plain login
mail_location = maildir:/var/mail/vhosts/%d/%n
mail_privileged_group = mail

namespace inbox {
  inbox = yes
  location =
  mailbox Drafts {
    special_use = \Drafts
  }
  mailbox Junk {
    special_use = \Junk
  }
  mailbox Sent {
    special_use = \Sent
  }
  mailbox "Sent Messages" {
    special_use = \Sent
  }
  mailbox Trash {
    special_use = \Trash
  }
  prefix =
}

passdb {
  args = /etc/dovecot/dovecot-sql.conf.ext
  driver = sql
}

protocols = imap lmtp

service auth-worker {
  user = vmail
}

service auth {
  unix_listener /var/spool/postfix/private/auth {
    group = postfix
    mode = 0666
    user = postfix
  }
  unix_listener auth-userdb {
    mode = 0600
    user = vmail
  }
  user = dovecot
}

service imap-login {
  inet_listener imap {
    port = 0
  }
}

service lmtp {
  unix_listener /var/spool/postfix/private/dovecot-lmtp {
    group = postfix
    mode = 0600
    user = postfix
  }
}

ssl = required
ssl_cert = </etc/letsencrypt/live/cermofi.cz/fullchain.pem
ssl_client_ca_dir = /etc/ssl/certs
ssl_dh = # hidden, use -P to show it
ssl_key = # hidden, use -P to show it

userdb {
  args = uid=vmail gid=vmail home=/var/mail/vhosts/%d/%n
  driver = static
}

Postfix 配置（执行 postconf -n 输出） #

alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
append_dot_mydomain = no
biff = no
compatibility_level = 3.6
inet_interfaces = all
inet_protocols = all
mailbox_size_limit = 0
mydestination = localhost
myhostname = cermofi.cz
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
myorigin = /etc/mailname
readme_directory = no
recipient_delimiter = +
relayhost =
smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
smtpd_recipient_restrictions = permit_sasl_authenticated, permit_mynetworks, reject_unauth_destination
smtpd_sasl_auth_enable = yes
smtpd_sasl_path = private/auth
smtpd_sasl_type = dovecot
smtpd_tls_cert_file = /etc/letsencrypt/live/cermofi.cz/fullchain.pem
smtpd_tls_key_file = /etc/letsencrypt/live/cermofi.cz/privkey.pem
smtpd_tls_loglevel = 3
smtpd_use_tls = yes
virtual_alias_maps = mysql:/etc/postfix/mysql-virtual-alias-maps.cf
virtual_mailbox_domains = mysql:/etc/postfix/mysql-virtual-mailbox-domains.cf
virtual_mailbox_maps = mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf
virtual_transport = lmtp:unix:private/dovecot-lmtp

遇到的问题 #

• 不带TLS的SMTP连接正常：用 telnet localhost 25 可以发送邮件
• 尝试TLS连接时失败：在telnet会话中输入STARTTLS后，直接收到 "Connection closed by foreign host."
• 连接Dovecot的IMAPS端口（993）也失败：telnet localhost 993 同样出现连接断开的错误
• 日志中的错误信息（来自/var/log/mail.log）：

Jan 30 17:29:45 cermofi-lab dovecot: imap-login: Disconnected: Connection closed: SSL_accept() failed: error:0A00010B:SSL routines::wrong version number (no auth attempts in 1 secs): user=<>, rip=127.0.0.1, lip=127.0.0.1, TLS handshaking: SSL_accept() failed: error:0A00010B:SSL routines::wrong version number, session=<kkgxRSwQwsx/AAAB>

Jan 30 17:37:05 cermofi-lab postfix/smtpd[41027]: warning: TLS library problem: error:0A00010B:SSL routines::wrong version number:../ssl/record/ssl3_record.c:354:
Jan 30 17:37:05 cermofi-lab postfix/smtpd[41027]: lost connection after STARTTLS from localhost[127.0.0.1]

• 证书本身是有效的：执行 openssl s_client -showcerts -connect cermofi.cz:993 -servername cermofi.cz 后，返回Verify return code: 0 (ok)，并且能正常看到Dovecot的就绪提示：

* OK [CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+ AUTH=PLAIN AUTH=LOGIN] Dovecot (Ubuntu) ready.

有没有大佬能帮我分析下为什么会出现这个SSL版本号错误呀？感谢！

备注：内容来源于stack exchange，提问作者cermofi