Ubuntu、postfix、dovecot 邮件服务器无法使用 Outlook 或 Thunderbird 邮件客户端进行配置

Question

我已成功使用 digital-ocean ubuntu 18.04 LEMP droplet 配置了我的电子邮件服务器，到目前为止一切正常。我可以发送和接收电子邮件，并且还成功配置了 round-cube 网络邮件客户端。我使用 Mailgun 作为 SMTP 中继。

但是当我尝试通过 Outlook 或 Thunderbird 连接到邮件服务器中的邮箱时，它一直说客户端找不到该帐户的设置。我尝试手动进行配置，但仍然出现相同的错误。

任何帮助或建议都将非常感激。

输出 postconf -n

alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
append_dot_mydomain = no
biff = no
compatibility_level = 2
dovecot_destination_recipient_limit = 1
inet_interfaces = all
inet_protocols = all
mailbox_size_limit = 0
mydestination = mail.myservername.com, localhost.localdomain, localhost
myhostname = myservername.com
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
readme_directory = no
recipient_delimiter = +
relayhost = [smtp.mailgun.org]:587
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = static:[email protected]:999999999-000000000000-9999999
smtp_sasl_security_options = noanonymous
smtp_tls_note_starttls_offer = yes
smtp_tls_security_level = may
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
smtpd_recipient_restrictions = permit_sasl_authenticated permit_mynetworks reject_unauth_destination
smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
smtpd_tls_cert_file = /etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file = /etc/ssl/private/ssl-cert-snakeoil.key
smtpd_tls_security_level = may
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtpd_use_tls = yes
virtual_mailbox_domains = myservername.com
virtual_transport = dovecot

输出 dovecot -n

mail_location = maildir:/var/mail/vmail/%d/%n/Maildir
mail_privileged_group = mail
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date index ihave duplicate mime foreverypart extracttext
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
}
plugin {
  sieve = file:~/sieve;active=~/.dovecot.sieve
}
protocols = " imap sieve"
service auth {
  unix_listener /var/spool/postfix/private/auth {
    group = postfix
    mode = 0660
    user = postfix
  }
  unix_listener auth-userdb {
    mode = 0666
    user = vmail
  }
  user = dovecot
}
service imap-login {
  inet_listener imap {
    port = 143
  }
}
service imap {
  process_limit = 1024
}
ssl_cert = </etc/dovecot/private/dovecot.pem
ssl_client_ca_dir = /etc/ssl/certs
ssl_key =  # hidden, use -P to show it
userdb {
  args = uid=vmail gid=vmail home=/var/mail/vmail/%d/%n
  driver = static
}
protocol lda {
  mail_plugins = " sieve"
}

sudo nmap your-server-ip给出以下输出：

PORT    STATE  SERVICE
22/tcp  open   ssh
80/tcp  open   http
443/tcp closed https
587/tcp open   submission