我已经为此搜索了解决方案，但没有一个解决了我的问题。我也在使用谷歌应用程序。
这是在 gmail 上收到的邮件的副本：
Delivered-To: suporte@taskka.com.br
Received: by 10.114.37.166 with SMTP id z6csp286681ldj;
Tue, 22 Jan 2013 17:22:28 -0800 (PST)
X-Received: by 10.236.119.206 with SMTP id n54mr27422481yhh.8.1358904147674;
Tue, 22 Jan 2013 17:22:27 -0800 (PST)
Return-Path: <contato@jetcarros.com.br>
Received: from smtp-web3-ctba.kinghost.net (smtp-web3-ctba.kinghost.net. [177.12.170.3])
by mx.google.com with ESMTP id h1si4616624anp.108.2013.01.22.17.22.26;
Tue, 22 Jan 2013 17:22:27 -0800 (PST)
Received-SPF: pass (google.com: domain of contato@jetcarros.com.br designates 177.12.170.3 as permitted sender) client-ip=177.12.170.3;
Authentication-Results: mx.google.com;
spf=pass (google.com: domain of contato@jetcarros.com.br designates 177.12.170.3 as permitted sender) smtp.mail=contato@jetcarros.com.br
Received: from smtp-web-ctba.kinghost.net (smtp-web-ctba [127.0.0.1])
by smtp-web3-ctba.kinghost.net (Postfix) with ESMTP id 7C5D58F2AE
for <suporte@taskka.com.br>; Tue, 22 Jan 2013 23:22:26 -0200 (BRST)
Received: from web593.kinghost.net (unknown [10.27.86.33])
by smtp-web-ctba.kinghost.net (Postfix) with ESMTP id 7BB2BC2DFC6C
for <suporte@taskka.com.br>; Tue, 22 Jan 2013 23:22:26 -0200 (BRST)
Received: by web593.kinghost.net (Postfix, from userid 850)
id 77EA6E9B6; Tue, 22 Jan 2013 23:22:26 -0200 (BRST)
To: suporte@taskka.com.br
Subject: test mail
From: contato@jetcarros.com.br
Subject: test mail
MIME-Version: 1.0
Content-Type: text/html; charset=UTF-8
Message-Id: <20130123012226.77EA6E9B6@web593.kinghost.net>
Date: Tue, 22 Jan 2013 23:22:26 -0200 (BRST)
It's a test mail<br/>
Another line<br/>
Yet another line.
和 jetcarros.com.br 上的 spf：
v=spf1 ip4:177.12.170.0/24 a mx a:jetcarros.com.br 包括:aspmx.googlemail.com ?all
在其他情况下，我发现人们说我可以通过将 php 邮件函数上的第 5 个参数设置为“-f$senderAdderess”来解决问题，但是信封发件人甚至不会像您一样出现在邮件的任何部分可以看上面。
这是我的脚本：
$email_content = implode ( "\n",array ( "It's a test mail", "Another line", "Yet another line.")
$email_headers = implode ( "\n",array ( "From: contato@jetcarros.com.br", "Subject: test mail","Return-Path: contato@jetcarros.com.br","MIME-Version: 1.0","Content-Type: text/html; charset=UTF-8" ) );
mail('suporte@taskka.com.br', 'test mail', nl2br($email_content), $email_headers, "-fcontato@jetcarros.com.br")
编辑：正如 iWizardPro 建议的那样，我使用 DKIM 来签署我的邮件，几个小时后让它正确签名，我已经完成了。但是我的电子邮件一直在垃圾邮件文件夹中。
欢迎在这里提供任何帮助。