Please refer to the Gmail sender guidance.
Reasons of Failed Delivery
In general, sending fails for one or more of the following reasons:
Too many emails sent
Sharp increase in the number of emails sent
Send emails to an unknown "spam honeypot address"
Send emails to an invalid address
The export IP is blacklisted
Emails sent are reported or marked as spam by Gmail users
Use a new IP to send emails without warming up
Incomplete /wrong DNS parsing records for domain
Email authentication failed
Include special attachment types/ IP links
What You Should Do Based on the Latest Google Delivery Advice
1. Verify your domain:
Google wants to receive authenticated emails. For users with a sending volume greater than 5000 (according to the statistics of the primary domain), the following three protocols must be configured.
a. SPF record
Purpose: To prevent others from maliciously using the same sending account on the Direct Mail platform to send notifications and promotional information under false names.
How to configure: The user modifies the TXT record of the domain name according to the configuration table in the Direct Mail Console in DNS service provider.
For more information, please refer to Configure the Domain Name of A Sender.
b. DKIM records
Purpose: An email security protocol that verifies the sending domain name of the email through message encryption and authentication, and is used to check whether the email has been tampered with during transmission to ensure the integrity of the body.
How to configure: The user follows the Direct Mail Console configuration table to modify the TXT record of a specific DKIM domain name in DNS service provider.
Reference Documentation: What is DKIM? How to Setup DKIM Records?
c. DMARC records
Purpose: It prevents forgery and informs the recipient how to handle forged emails and obtains forged information.
How to configure: The user adds a TXT record in the format of v=DMARC1;p=none; Rua=mailto:a***@example.net; Ruf=mailto:a***@example.net in DNS service provider. The email addresses set for Rua and Ruf are configured by the user.
2. Add Unsubscribe Method
Gmail requires that marketing addresses with a volume of more than 5,000 messages must be provided with a one-click unsubscribe button for the recipient. Please refer to The Description of the Unsubscription Function.
3. Use the Google postmaster tool to continuously monitor the reputation and report status of your domain name management page, and configure the DNS according to the specific value given by Gmail to complete Gmail's verification of domain name ownership.
a. Google requires that the spam_report_rate should be kept below 0.1%. If it is higher than 0.3%, Google will impose penalties. In our experience, penalties can lead to a decline in the credibility of the domain name, resulting in subsequent emails being rejected or going to the trash.
b. The postmaster tool information has lag. Today's delivery status and credibility need to be checked in 2-3 days. If the delivery volume is too small, there will be no postmaster information. It is recommended that the delivery volume should be more than 500 per day.
4. Use the warm-up plan and gradually increase the number of messages sent. For more information, please refer to Warm-up Suggestions.
5. Check the status of your domain names on Google
6. Use the troubleshooting tool
If you are still experiencing mail delivery issues after following the guidelines in this article, please try to troubleshoot sender email delivery issues