Gmail Blocks Messages

Gmail Postmaster Tools provides senders with metrics on parameters such as reputation, spam rate, feedback loop, etc. It can help you prevent your emails from being blocked or sent to spam by Gmail.

Gmail works hard to fight spam. While in some cases they may classify a message as spam and deliver it to the spam folder, they also try to find ways to reduce the amount of spam being sent to Gmail in general. If they detect that a message has a strong likelihood of being spam, they’ll block the message from being sent to Gmail. A message might be blocked if it contains suspicious-looking or spammy text or if the sending IP has had a history of sending unsolicited messages.

Is all of the mail I’m sending being blocked? It’s likely that only a subset of the messages which have a strong likelihood of being spam are being blocked and not all of your messages. However, to help improve your deliverability, we recommend reviewing their Bulk Sender Guidelines. If you’re forwarding mail to Gmail and your domain also forwards spam, we recommend reviewing the mail forwarding best practices.

POSTMASTER TOOLS

If you send a large volume of emails to Gmail users, you can use Postmaster Tools to see:

If users are marking your emails as spam
How to prevent your emails from being blocked by Gmail
Why your emails might not be delivered
If your emails are being sent securely

Add & verify your Authentication Domains

An authentication domain is either the DKIM (d=) or SPF domain (Return-Path domain) that is used to authenticate your email. You can find it in the ‘Authentication Results’ header of an email that has successfully passed authentication (and was delivered to a Gmail mailbox).

For example, in the sample Authentication Results header below, domain.com is the ‘Authentication Domain.’:
Authentication-Results: mx.google.com;
spf=pass (google.com: domain of bounce-123@domain.com designates 1.2.3.4 as permitted sender)
dkim=pass header.i=@domain.com;
DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; s=12345; d=domain.com;

Postmaster Tools uses your authentication domain to uniquely identify your email traffic and provide access to your traffic analytics.

Tip: Authentication domain can be either the domain-name or the sub-domain. If it’s a domain-name, the data will show the traffic aggregated over any and all sub-domains of that domain-name, plus any traffic corresponding to the (exact) domain-name match. You can also independently add multiple sub-domains and view data about each of them separately.

Add a domain:

Go to postmaster.google.com.
On the bottom-right, click the + button.
In the box that pops up, enter your authentication domain.
Next, prove that you own the domain by adding a DNS TXT or a DNS CNAME record.

Each account needs a separate DNS verification record, and you won’t be able to see your traffic analytics until you complete this step.

SPF RECORD TESTING

SPF Record Testing help you deploy SPF records for your domain. They use an actual RFC 7208 compliant library (pyspf) for tests and will dynamically test for processing limit errors. This site uses a caching DNS resolver, so for tests that use live DNS, results will be cached for the Time To Live of the DNS record. For most basic uses, these tests should be reasonably self explanatory. Advanced users may need, and probably want, some additional information on how these tools work. It can be found here.