Gmail to or - Spam Filter issue

Post date: Jun 19, 2018 9:37:58 PM

We use the Google Suite for our hosted email. Up until recently an email to an address would have appeared to have been delivered to the recipient's inbox, but instead was actually being deleted by Comcast upon receipt from Google's email servers.

We were actually being blocked by the Comcast spam filter. Most of our messages were just going in to a black hole and not even seen in the recipient's spam folder. There is a setting you have to engage in the settings of your Comcast mailbox that saves spam. If you don't set it, Comcast just deletes it offhand. Once an email is flagged as spam, and you have that setting engaged, the folder captures the message. The user can then go in and individually mark an email as "not spam". Then the message can be moved back to the inbox.

Comcast is not alone in this strict behavior, a few other vendors have stepped up their game in spam filtration, and anything from Google's email servers, including it's own domain are scrutinized at a much higher level and may or may not be delivered as expected.

For example, Centurylink(, they, instead of a black hole, will just bounce back with:

The response from the remote server was: 554 5.7.1 [P4] Message blocked due to spam content in the message.

What I found by playing with the issue, is that if I created a normal email to someone and sent it, and they said they didn't receive it, I would craft it again, but this time, I would select all text, and then hit the Tx button in the Google email tool. That button turns the message in to Plain Text. Make sure to keep it that way, and click send. If they receive the message, then you can confirm that your domain is being blocked because of 'spam content'. The spam content in this case is really just the use of HTML. Not really spam. It's a false positive that you pay the price for. The settings at Comcast and are just higher than everyone else.

So... The First thing you need to do is search the Blacklists, and see if you are on any of them. Just to make sure this isn't a more global issue. MXToolBox is a great resource for most of your needs here. If you come back clean, then proceed on.

The second thing to do is to look at your SPF record. Sender Policy Framework (SPF) records allow domain owners to publish a list of IP addresses or subnets that are authorized to send email on their behalf. The goal is to reduce the amount of spam and fraud by making it much harder for malicious senders to disguise their identity. Make sure to limit yourself to a max of 10 IP addresses.

Next you want to make sure you have DKIM set up and authenticating your messages. DomainKeys Identified Mail (DKIM) lets an organization take responsibility for a message that is in transit. The organization is a handler of the message, either as its originator or as an intermediary. Their reputation is the basis for evaluating whether to trust the message for further handling, such as delivery. Technically DKIM provides a method for validating a domain name identity that is associated with a message through cryptographic authentication.Set it to the highest allowed setting. Ensure that the control panel says it's authenticating, then check the behavior with an MX DKIM tool.

Lastly, you need to set up DMARC. DMARC, which stands for “Domain-based Message Authentication, Reporting & Conformance”, is an email authentication, policy, and reporting protocol. It builds on the widely deployed SPF and DKIM protocols, adding linkage to the author (“From:”) domain name, published policies for recipient handling of authentication failures, and reporting from receivers to senders, to improve and monitor protection of the domain from fraudulent email.Confirm its working and reporting. Note: It takes about 48 hours once you have everything up and working, but after replication of all your changes, the email servers at Comcast and Q will start trusting your HTML emails once again.

Handy tool by Google for checking your domain:

To look up SMTP Error messages related to gmail, use this link: