==== 必填信息。没有填写将不予回复 ====
- iRedMail 版本号：0.9.7
- 使用哪个数据库存储用户帐号（OpenLDAP，MySQL，PostgreSQL）：MySQL
- 使用的 Linux/BSD 发行版名称及版本号：Ubuntu 16.04LTS
- 与您的问题相关的日志信息：

域内可以收发邮件，域外只能收不能发；
搭建之后使用了 Let's Encrypt 提供免费的 SSL 证书；
下面是/var/log/mail.log中全部信息

Jul 18 14:23:22 mail postfix[10713]: Postfix is running with backwards-compatible default settings
Jul 17 14:23:22 mail postfix[10713]: See http://www.postfix.org/COMPATIBILITY_README.html for details
Jul 17 14:23:22 mail postfix[10713]: To disable backwards compatibility use "postconf compatibility_level=2" and "postfix reload"
Jul 17 14:23:22 mail postfix/master[10758]: daemon started -- version 3.1.0, configuration /etc/postfix
Jul 17 14:23:48 mail dovecot: master: Dovecot v2.2.22 (fe789d2) starting up without any protocols (core dumps disabled)
Jul 17 14:23:48 mail dovecot: ssl-params: Generating SSL parameters
Jul 17 14:23:55 mail dovecot: ssl-params: SSL parameters regeneration completed
Jul 17 14:24:30 mail amavis[26100]: starting. /usr/sbin/amavisd-new at mail.licte.cn amavisd-new-2.10.1 (20141025), Unicode aware, LC_ALL="C", LANG="en_US.UTF-8"
Jul 17 14:24:30 mail amavis[26107]: Net::Server: Group Not Defined.  Defaulting to EGID '127 127'
Jul 17 14:24:30 mail amavis[26107]: Net::Server: User Not Defined.  Defaulting to EUID '116'
Jul 17 14:24:30 mail amavis[26107]: Module Amavis::Conf        2.404
Jul 17 14:24:30 mail amavis[26107]: Module Archive::Zip        1.56
Jul 17 14:24:30 mail amavis[26107]: Module BerkeleyDB          0.55
Jul 17 14:24:30 mail amavis[26107]: Module Compress::Raw::Zlib 2.068
Jul 17 14:24:30 mail amavis[26107]: Module Compress::Zlib      2.068
Jul 17 14:24:30 mail amavis[26107]: Module Crypt::OpenSSL::RSA 0.28
Jul 17 14:24:30 mail amavis[26107]: Module Digest::MD5         2.54
Jul 17 14:24:30 mail amavis[26107]: Module Digest::SHA         5.95
Jul 17 14:24:30 mail amavis[26107]: Module Encode              2.72
Jul 17 14:24:30 mail amavis[26107]: Module File::Temp          0.2304
Jul 17 14:24:30 mail amavis[26107]: Module IO::Socket::INET6   2.72
Jul 17 14:24:30 mail amavis[26107]: Module IO::Socket::IP      0.37
Jul 17 14:24:30 mail amavis[26107]: Module MIME::Entity        5.507
Jul 17 14:24:30 mail amavis[26107]: Module MIME::Parser        5.507
Jul 17 14:24:30 mail amavis[26107]: Module MIME::Tools         5.507
Jul 17 14:24:30 mail amavis[26107]: Module Mail::DKIM::Signer  0.4
Jul 17 14:24:30 mail amavis[26107]: Module Mail::DKIM::Verifier 0.4
Jul 17 14:24:30 mail amavis[26107]: Module Mail::Header        2.13
Jul 17 14:24:30 mail amavis[26107]: Module Mail::Internet      2.13
Jul 17 14:24:30 mail amavis[26107]: Module Net::DNS            0.81
Jul 17 14:24:30 mail amavis[26107]: Module Net::LibIDN         0.12
Jul 17 14:24:30 mail amavis[26107]: Module Net::Server         2.008
Jul 17 14:24:30 mail amavis[26107]: Module Scalar::Util        1.41
Jul 17 14:24:30 mail amavis[26107]: Module Socket              2.018
Jul 17 14:24:30 mail amavis[26107]: Module Socket6             0.25
Jul 17 14:24:30 mail amavis[26107]: Module Time::HiRes         1.9726
Jul 17 14:24:30 mail amavis[26107]: Module Unix::Syslog        1.1
Jul 17 14:24:30 mail amavis[26107]: Amavis::ZMQ code     NOT loaded
Jul 17 14:24:30 mail amavis[26107]: Amavis::DB code      loaded
Jul 17 14:24:30 mail amavis[26107]: SQL base code        NOT loaded
Jul 17 14:24:30 mail amavis[26107]: SQL::Log code        NOT loaded
Jul 17 14:24:30 mail amavis[26107]: SQL::Quarantine      NOT loaded
Jul 17 14:24:30 mail amavis[26107]: Lookup::SQL code     NOT loaded
Jul 17 14:24:30 mail amavis[26107]: Lookup::LDAP code    NOT loaded
Jul 17 14:24:30 mail amavis[26107]: AM.PDP-in proto code loaded
Jul 17 14:24:30 mail amavis[26107]: SMTP-in proto code   loaded
Jul 17 14:24:30 mail amavis[26107]: Courier proto code   NOT loaded
Jul 17 14:24:30 mail amavis[26107]: SMTP-out proto code  loaded
Jul 17 14:24:30 mail amavis[26107]: Pipe-out proto code  NOT loaded
Jul 17 14:24:30 mail amavis[26107]: BSMTP-out proto code NOT loaded
Jul 17 14:24:30 mail amavis[26107]: Local-out proto code loaded

====