Why is gmail marking my email as spam?

Question

I have a VPS (Droplet) at DigitalOcean. I am sending mail from a website, but I have configured PHP to use my SMTP server instead of just the usual PHP Mail().

I have DKIM, DMARC, SPF configured correctly.

Here are some of the relevant headers in my message:

Received-SPF: pass (google.com: domain of stockapi@lfto.me designates 104.236.231.177 as permitted sender) client-ip=104.236.231.177;

Authentication-Results: mx.google.com;
       spf=pass (google.com: domain of stockapi@lfto.me designates 104.236.231.177 as permitted sender) smtp.mailfrom=stockapi@lfto.me;
       dkim=pass header.i=@lfto.me;
       dkim=pass header.i=@lfto.me;
       dmarc=pass (p=QUARANTINE dis=NONE) header.from=lfto.me
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=lfto.me; s=mail;
    t=1452989846; bh=czrEg02FSPEvWjTq3enrcAZrxmaNPmFuwA/aUIJ/fNY=;
    h=From:To:Date:Subject:From;
    b=hQ/09WMZxJO692Lg7g/1TmOLbwWp2rMoHhl/P5Eb6auvhIjDG6tEYxgksg5qYBYEq
     4NmPO9yddeW/JqLHCL4GWFafYGXorfA6oR/uqwwI0Jt6aflEJunFEVxxon8jvxiVp5
     BsuxdU0vu7GPDH289L3Lf3/oG1nKrn22L2PcKreo=

According to these, it seems my message is passing all checks, but still is getting into the "spam" folder. What could be the problem?

Answer 1

似乎大多数未列出的电子邮件（该列表由Google保留）的IP地址都将转到Gmail中的垃圾文件夹，即使已发送的电子邮件根据SMTP也有效。

Answer 2

Chiefly, to avoid a spam engine classifying your messages as spam you should:

Make sure they aren't spam (ie ensure that only users who have really opted in get mailed - make sure you keep an opt-in audit log)Make sure they don't look too much like spam - $$$ MAKE MONEY FAST is not a good subject lineEnsure that the sender address is not spoofed and does not appear to be spoofed. Use a domain that you are authorised to send from (add valid SPF records if you like)Not do anything that looks malware-ish (eg HTML emails containing scripts, forms, flash etc)

But by and large the main one is:

Do not send them from an IP address which is known for sending spam.

The last point means that YOU CANNOT USE SHARED HOSTING. Almost all shared hosting providers allow the sending of mails which don't conform to any of the above. Shared hosting providers' relays are almost always on lots of blacklists.

It only takes one vulnerable web app on your shared hosting for it to turn into a spam gateway - something which you can't afford.