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SPF and DKIM are failing DMARC test
When setting up your SMTP you need to ensure the DMARCs Return-Path matches the domain in your From address. If not, the SPF and DKIM configuration would fail the DMARC alignment test.
In this case, You can set up a DKIM record and check with this source about setting up the custom Return-Path.
Note: Chargebee does not support signing mails with other domains while sending. To use DMARC, you can verify your domain (DKIM) in the postmarkapp and use its SMTP credentials in Chargebee to avoid this issue.
Kindly make sure you adhere to the following settings when you set up the SMTP configuration.
Create a custom app credential, if your account has Multiple factor authentication (MFA) enabled.
Check for overrides in Mail clients' SMTP account ‘From Address' & the 'From address' you set in Chargebee
For some email clients, such as Office 365, the username of the ‘SMTP Settings' and the ‘From Address' given in Chargebee should be the same, for you to use the credentials in Chargebee.
If you have configured your own SMTP, we would not have access to the logs to check the delivery of the emails.
Make sure the email address that you bcc to is a “catch-all” email address that forwards the email to your individual accounts.
If you have enabled DMARC for your domain then you will need to use your own SMTP server where you have verified DKIM and SPF records for your domain with respect to the SMTP provider, making the SMTP provider an authenticated sender on your behalf.
Once you have created your own SMTP server, you can configure that SMTP credentials in Chargebee so that your emails don't get dropped due to DMARC checks.
DMARC is built upon two authentication protocols- DKIM and SPF and you need to mention both on your domains before proceeding with DMARC.
You can refer to this document for more information.