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Outgoing emails sent from a Plesk server to mail services like Gmail, Yahoo, Outlook go to the spam folder. How to troubleshoot?
Note: This guide is intended for Plesk administrators. If you are a domain owner, please contact your service provider for assistance.
Here is the list of the most common reasons why it may happen:
SPF/DKIM/DMARC features are not configured in Plesk.
An email content matches spam description. For example, an empty email message will be marked as spam.
Server IP address is blacklisted.
If a sender's email account is used for sending email notifications and other users mark these messages as spam, there is a high probability that these emails will go to the spam folder for other users as Gmail has learning algorithms;
How to troubleshoot
If some warnings are detected, verify that everything is configured properly:
Make sure there is a TXT SPF record in domain's DNS settings at Domains > example.com > DNS Settings:
Note: By default, a SPF record is added to the domain's DNS zone during a domain creation in accordance with the Plesk DNS Template.
To learn more about SPF, visit this KB article.
Make sure there is a TXT DMARC record in domain's DNS settings at Domains > example.com > DNS Settings::
Note: By default, a DMARC record is added to the domain's DNS zone during a domain creation in accordance with the Plesk DNS Template.
To learn more about DMARC, visit its overview page.
Make sure that DKIM support is enabled server-wide in Plesk at Tools & Settings > Mail Server Settings:
Make sure that DKIM support is enabled for a domain in at Domains > example.com > Mail Settings:
Finally, verify that necessary records are present in domain's DNS settings:
To learn more about DKIM, SPF, and DMARC Protection, visit this Plesk documentation page.
Note: In case of multiple DKIM keys are configured, verify that they are set on different selectors (default._domainkey.example.com, new._domainkey.example.com, etc.)
If an external DNS server is used for a domain, make sure that all TXT records related to DKIM and DMARC (default._domainkey.<example.com>, _domainkey.<example.com>, _dmarc.<example.com>) from domain's DNS settings are transferred to external DNS as is.
Validate content of the message that was marked as spam. Common message attributes that can trigger spam filters:
The body of the message is empty or contains spam trigger words like:
PLESK_INFO: amazing, cancel at any time, check or money order, click here, congratulations, dear friend, for only ($), free or toll-free, great offer, guarantee, increase sales, order now, promise you, risk free, special promotion, this is not spam, winner
- Suspicious subject of the message, like "How to become a billionaire in 1 month"
Once done with the steps above, try to send a test email to a mail service like Gmail, Outlook, Yahoo! Mail, etc. If this email still hits the Spam folder there, contact support of a mail service to remove your IP address from their blacklists: