搞明白了,因为我用的VPS目前在试用期间,
试用期间port25被禁用了:(

==== 必填信息。没有填写将不予回复 ====
- iRedMail 版本号:    v0.9.5-1
- 使用哪个数据库存储用户帐号(OpenLDAP,MySQL,PostgreSQL):OpenLDAP
- 使用的 Linux/BSD 发行版名称及版本号:Centos7.1
- 与您的问题相关的日志信息:
====
Dec 27 11:12:43 mail postfix/submission/smtpd[4609]: connect from xxx.st.wakwak.ne.jp[61.115.125.xxx]
Dec 27 11:12:43 mail postfix/submission/smtpd[4609]: Anonymous TLS connection established from verisoft.st.wakwak.ne.jp[61.115.125.133]: TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits)
Dec 27 11:12:43 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 203 bytes to sd 11
Dec 27 11:12:43 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 222 bytes to sd 11
Dec 27 11:12:43 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 206 bytes to sd 11
Dec 27 11:12:43 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 211 bytes to sd 11
Dec 27 11:12:43 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 230 bytes to sd 11
Dec 27 11:12:43 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 214 bytes to sd 11
Dec 27 11:12:43 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 197 bytes to sd 11
Dec 27 11:12:43 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 191 bytes to sd 11
Dec 27 11:12:43 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 187 bytes to sd 11
Dec 27 11:12:43 mail postfix/submission/smtpd[4609]: A495C124C2: client=xxx.st.wakwak.ne.jp[61.115.125.xxx], sasl_method=LOGIN, sasl_username=xxx@mailserver.com
Dec 27 11:12:43 mail postfix/cleanup[4611]: A495C124C2: message-id=<005801d25fe6$a0602ce0$e12086a0$@mailserver.com>
Dec 27 11:12:43 mail postfix/qmgr[4589]: A495C124C2: from=<xxx@mailserver.com>, size=1041, nrcpt=1 (queue active)
Dec 27 11:12:44 mail postfix/smtpd[4615]: connect from mail.mailserver.com[127.0.0.1]
Dec 27 11:12:44 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 203 bytes to sd 11
Dec 27 11:12:44 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 222 bytes to sd 11
Dec 27 11:12:44 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 206 bytes to sd 11
Dec 27 11:12:44 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 211 bytes to sd 11
Dec 27 11:12:44 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 230 bytes to sd 11
Dec 27 11:12:44 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 214 bytes to sd 11
Dec 27 11:12:44 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 197 bytes to sd 11
Dec 27 11:12:44 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 191 bytes to sd 11
Dec 27 11:12:44 mail postfix/smtpd[4615]: 4E1CC124C5: client=mail.mailserver.com[127.0.0.1]
Dec 27 11:12:44 mail postfix/cleanup[4611]: 4E1CC124C5: message-id=<005801d25fe6$a0602ce0$e12086a0$@mailserver.com>
Dec 27 11:12:44 mail postfix/smtpd[4615]: disconnect from mail.mailserver.com[127.0.0.1]
Dec 27 11:12:44 mail postfix/qmgr[4589]: 4E1CC124C5: from=<xxx@mailserver.com>, size=2126, nrcpt=1 (queue active)
Dec 27 11:12:44 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 211 bytes to sd 11
Dec 27 11:12:44 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 230 bytes to sd 11
Dec 27 11:12:44 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 214 bytes to sd 11
Dec 27 11:12:44 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 197 bytes to sd 11
Dec 27 11:12:44 mail postfix/proxymap[4590]: dict_ldap_debug: ber_flush2: 191 bytes to sd 11
Dec 27 11:12:44 mail amavis[2654]: (02654-05) Passed CLEAN {RelayedInternal}, ORIGINATING LOCAL [61.115.125.xxx]:3096 [61.115.125.133] <xxx@mailserver.com> -> <yyy@toserver.co.jp>, Queue-ID: A495C124C2, Message-ID: <005801d25fe6$a0602ce0$e12086a0$@mailserver.com>, mail_id: VDIY5QivziDC, Hits: -0.999, size: 1041, queued_as: 4E1CC124C5, dkim_new=dkim:mailserver.com, 565 ms, Tests: [ALL_TRUSTED=-1,URIBL_BLOCKED=0.001]
Dec 27 11:12:44 mail postfix/smtp[4612]: A495C124C2: to=<yyy@toserver.co.jp>, relay=127.0.0.1[127.0.0.1]:10026, delay=0.7, delays=0.12/0.01/0/0.57, dsn=2.0.0, status=sent (250 2.0.0 from MTA(smtp:[127.0.0.1]:10025): 250 2.0.0 Ok: queued as 4E1CC124C5)
Dec 27 11:12:44 mail postfix/qmgr[4589]: A495C124C2: removed
Dec 27 11:12:46 mail postfix/submission/smtpd[4609]: disconnect from xxx.st.wakwak.ne.jp[61.115.125.xxx]
Dec 27 11:13:14 mail postfix/smtp[4592]: connect to toserver.co.jp[61.126.19.xxx]:25: Connection timed out
Dec 27 11:13:14 mail postfix/smtp[4592]: 4E1CC124C5: to=<yyy@toserver.co.jp>, relay=none, delay=30, delays=0.01/0.01/30/0, dsn=4.4.1, status=deferred (connect to toserver.co.jp[61.126.19.xxx]:25: Connection timed out)

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给自己的邮件域名发邮件没有问题,
但是往其他域名的邮件地址发邮件失败(SMTP/IMAP都实验过,均失败)。
收邮件没有问题。