Why are our Gmail customers receiving a pop-up stating: "Gmail couldn't verify that this message was sent by domain.com"?
Oracle B2C Service, All versions
This behavior is a specific post updating SPF record on the customer mailboxes, and usually caused by SPF (SPF1) and Sender ID (SPF2) records not being the same.
Message: Gmail couldn't verify that this message was sent by <domain.com>
More information about SPF records can be found in SPF and Sender ID considerations with Oracle B2C Service sites.
We recommend engaging your Email and Messaging department when undertaking such operations.
Once you update the SPF1 AND SPF2 records to reflect the correct information, it will take some time for the settings to be propagated to the Gmail server. The pop-up message will disappear retroactively on all the e-mails which you sent while using the wrong settings.