後綴：所有出站電子郵件上的“連接超時”

Aug 25 12:56:20 mail postfix/pickup[375941]: ACF7F200E248: uid=0 from=<root>
Aug 25 12:56:20 mail postfix/cleanup[376172]: ACF7F200E248: message-id=<20210825125620.ACF7F200E248@mail.localdomain>
Aug 25 12:56:20 mail postfix/qmgr[375942]: ACF7F200E248: from=<root@mail.localdomain>, size=449, nrcpt=1 (queue active)
Aug 25 12:56:20 mail postfix/smtp[377199]: connect to gmail-smtp-in.l.google.com[2a00:1450:400c:c06::1a]:25: Network is unreachable
Aug 25 12:56:31 mail postfix/smtp[376174]: connect to alt1.gmail-smtp-in.l.google.com[142.251.9.27]:25: Connection timed out
Aug 25 12:56:31 mail postfix/smtp[376174]: connect to alt1.gmail-smtp-in.l.google.com[2a00:1450:4025:c03::1b]:25: Network is unreachable
Aug 25 12:56:31 mail postfix/smtp[376174]: connect to alt2.gmail-smtp-in.l.google.com[2a00:1450:4010:c1c::1a]:25: Network is unreachable
Aug 25 12:56:31 mail postfix/smtp[376174]: E2CD82020B3F: to=<example@gmail.com>, relay=none, delay=60, delays=0.03/0.03/60/0, dsn=4.4.1, status=deferred (connect to alt2.gmail-smtp-in.l.google.com[2a00:1450:4010:c1c::1a]:25: N>
Aug 25 12:56:50 mail postfix/smtp[377199]: connect to gmail-smtp-in.l.google.com[66.102.1.26]:25: Connection timed out
Aug 25 12:56:50 mail postfix/smtp[377199]: connect to alt1.gmail-smtp-in.l.google.com[2a00:1450:4025:c03::1b]:25: Network is unreachable

我使用 VPS azure（Centos 8），我線上檢查了埠 25 但沒有被阻止（工作），我使用 telnet 檢查了埠

$ telnet 51.xx.xx.xx 25
output:
220 mail.localdomain ESMTP Postfix

對於大多數客戶，Azure 會阻止埠 25 上的出站 SMTP 。

引用自：https://serverfault.com/questions/1075609