Tenho um servidor de email em CentOS, e começou a bloquear os emails do servidor GMAIL. O que será que aconteceu?

Já olhou os logs? Posta eles ai.

This is an automatically generated Delivery Status Notification

THIS IS A WARNING MESSAGE ONLY.

YOU DO NOT NEED TO RESEND YOUR MESSAGE.

Delivery to the following recipient has been delayed:

xxxxxxxx@xxxxxxxx.xxx.br

Message will be retried for 2 more day(s)

Technical details of temporary failure:
Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 451 451 4.7.1 Service unavailable - try again later (state 17).

----- Original message -----

DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
d=gmail.com; s=20120113;
h=mime-version:date:message-id:subject:from:to:content-type;
bh=yLy0VH6EdSi2B5WQ9To2DPuddhAYMeiqDmLAjUXN9/s=;
b=HzPMFWHkUn11s7OzqaOyBiZRobY44go2BJ8tBsuuXGoOtLHVTo6dqHbl90P0GJcAph
01UQEDdPHbcVXYvwIB0HEoCffavX3iU+KPfp9zYHcSf4Qy0eb3XLMD+1elqGIJFOHEdz
gMGZsQ/cBVVX8hpVbUWnyz+PByGgPRwI61+cFEncuPWRPzIK9bVB0zidTQu488C2x9Tn
t8t+ZfxgxSFKwqH7cUG04cum2kMee+cPeLEA1QbYFiVZZuhQIpBF7+030iyCp8KLMKmu
84brrDbaL+agp3EwWS6Twh38iuv3lnq0hxrDBUov4lvrJB0wHiyUlChqehScO2LZalX6
cxkQ==
MIME-Version: 1.0
Received: by 10.216.211.19 with SMTP id v19mr9158275weo.89.1339004206266; Wed,
06 Jun 2012 10:36:46 -0700 (PDT)
Received: by 10.216.192.66 with HTTP; Wed, 6 Jun 2012 10:36:46 -0700 (PDT)
Date: Wed, 6 Jun 2012 14:36:46 -0300
Message-ID: <CAChE9wEf6fVqLzS7dd+Ki3+_HRAtpOW1wAigCLiHddLFgU=2AA@mail.gmail.com>
Subject: teste 2
From: xxxxxxxxxxxxxxxxxxx <xxxxxxxxxxxxxxxx@gmail.com>
To: xxxxxx <xxxxxx@xxxxxxxxxxx.xxxx.br>
Content-Type: multipart/alternative; boundary=0016e6dbe9321139d704c1d1365d

agora

Ele não consegue entregar no seu server. Primeira coisa que eu faria é ver se a porta 25 está ok.

Teste:

http://www.mxtoolbox.com/diagnostic.aspx

Veja se retorna algum erro.

Mais algumas informações:

Códigos 451 e 451 4.7.1

451 Requested action aborted: local error in processing (the service can not access the assigned \temp\ folder)

451 4.7.1 This server is currently unavailable, please try later. (This is returned when Greylisting is enabled in AntiSpam)

Veja os logs do sei mail.log.

No CentOS deve ser algo assim:

# tail -100 /var/log/maillog

Obs; está recusando somente o GMAIL, demais servidores está recebendo normal (hotmail, yahoo...)

Jun 8 10:54:55 server3 postfix/policy-spf[26061]: : SPF pass (Mechanism ´ip4:209.85.128.0/17´ matched): Envelope-from: xxxxxx@gmail.com
Jun 8 10:54:55 server3 postfix/policy-spf[26061]: : Policy action=PREPEND Received-SPF: pass (gmail.com... _spf.google.com: 209.85.212.173 is authorized to use ´xxxxxx@gmail.com´ in ´mfrom´ identity (mechanism ´ip4:209.85.128.0/17´ matched)) receiver=server3.empresa.coop.br; identity=mailfrom; envelope-from=xxxxxxx@gmail.com"; helo=mail-wi0-f173.google.com; client-ip=209.85.212.173
Jun 8 10:54:56 server3 postfix/policy-spf[26061]: B6A8D535774: milter-reject:END-OF-MESSAGE from mail-w10-f173.google.com[209.85.212.173]: 4.7.1 Service unavailable - try again later; from=<xxxxxxxx@gmail.com> to=<bbbb@empresa.coop.br>

Entendi. Olha as regras desse cara ai "postfix/policy-spf".

Verifiquei as regras e está tudo certo, inclusive não houve alteração no arquivo, desde a implantação do servidor há uns 2 anos.

Faz o seguinte. Comente suas politicas e restarte o postfix. Se não houver ligação vai dar o mesmo erro.

Comentei somente a política de recipiente. Das 3 mensagens que estavam aparecendo,a mensagem abaixo permanece:

Jun 8 16:54:56 server3 postfix/policy-spf[4969]: 05C15535764: milter-reject:END-OF-MESSAGE from mail-w10-f51.google.com[74.125.82.51]: 4.7.1 Service unavailable - try again later; from=<xxxxxxxx@gmail.com> to=<bbbb@empresa.coop.br>

Comenta a linha policy-spf no master.cf, restarte o postfix e teste novamente.

Ex:

Após comentar a linha, a mensagem é a seguinte:

Jun 11 08:19:40 server3 postfix/smtpd[12904]: NOQUEUE: reject: RCPT from mail-wg0-f51.google.com[74.125.85.51]: 451 4.3.5 Server configuration problem; from=<aaaaaaa@gmail.com> to=bbbbbb@empresa.coop.br> proto=ESMTP helo=<mail -wg0-f51.google.com>
Jun 11 08:19:44 server3 postfix/smtpd[12892]: NOQUEUE: reject: RCPT from mail-wi0-f179.google.com[209.85.212.179]: 451 4.3.5 Server configuration problem; from=<aaaaaaa@gmail.com> to=bbbbbb@empresa.coop.br> proto=ESMTP helo=<mail -wi0-f179.google.com>