NB! As of February 2024, Gmail’s spam detection rules have changed. An SPF and DKIM record is required for the domain (more information below), and the requirements for domains that send 5,000 and more emails per day also changed. More information from Google articles:
Email sender guidelines:
https://support.google.com/a/answer/81126
Prevent spam, spoofing & phishing with Gmail authentication:
https://support.google.com/a/answer/10583557

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NOTE! As of June 7th, 2022, the Gmail service will not allow email to be sent to email addresses in Gmail, unless the sender’s domains DNS records contain working SPF and DKIM entries!

If you have received a return message that says:
550-5.7.1 [212.47.208 ....] Our system has detected that this message is likely unsolicited mail.
To reduce the amount of spam sent to Gmail, this message has been blocked.
Please visit https://support.google.com/mail/?p=UnsolicitedMessageError for more information.
Follow the instructions below to fix this through your cPanel webhosting account!

In order to increase the reliability of outgoing e-mails and to prevent e-mails from going to receivers spam folder, the domain should have valid and correct SPF and DKIM records.
To check these records, enter the cPanel environment and select “Email Deliverability” from the menu.
Make sure the domains have “Valid” in the “Email Deliverability Status” column.
If “Problems Exist” is listed instead, allow cPanel to add SPF and DKIM entries for the domain by clicking the “REPAIR” button.
If pressing the “REPAIR” button does not solve the situation, press the “MANAGE” button to add entries manually.
On the next page, select “Generate Local DKIM Key” under “DKIM” and then “Install The Suggested Record”.
Under “SPF” select “Install The Suggested Record”.

If you also send messages via another server, you can add the address of that server to the SPF record on this page.

The tool for creating SPF records can be found at the following address:
https://mxtoolbox.com/SPFRecordGenerator.aspx

NB! After adding or modifying SPF and DKIM records, it takes up to 1 hour for the new DNS records to propagate.

If you want to add/modify the SPF record directly in the cPanel Zone editor, you can add it:
cPanel -> DOMAINS -> Zone Editor -> click on your domain in the “Manage” line then “Add a record” and add a TXT type record, where the first box should contain your domain name without the www prefix and the last box as:

v = spf1 a mx include: _spf.radicenter.eu -all

NB! If you have updated/fixed the SPF information for Your domain due to a Gmail problem, we would additionally recommend to:
1. Go to the https://developers.google.com/speed/public-dns/cache
2. Enter the name of your own domain (in the format of domainname.eu) in the box
3. Select A, MX, TXT per try from the dropdown and click the “Flush Cache” button (i.e. those 3 entries and clicking the button should update Google DNS cache and fix should work faster!)