You might have set up a Sender Policy Framework (SPF) record for your domain but your emails are still being captured as SPAM. This article provides information on how to fix this issue.
There could be different reasons why this issue may occur but one of the most common ones is that the SPF record exceeds the 10 DNS query limit.
Keep in mind that your SPF record should not exceed the 10 DNS query limit. Exceeding this limit will result in deteriorated email deliverability. Hence, emails might still be detected as SPAM even though you have configured an SPF record for your domain.
The number of "include" mechanisms and chained "redirect' modifiers should be kept to a minimum, or at most 10 per SPF record. You can use an online SPF Checker such as the following to check your SPF record:
The details on how to set up an SPF record can be found in Ensuring Your Emails Are Received and Do Not Go Into Your Customer's Spam Folder article.