Emails are not related to the intended Salesforce records when using the Salesforce for Outlook plugin, Outlook Integration (for logging Emails on Send), or Email to Salesforce. There is also no bounce back email sent when this occurs.
When emails are sent to a record in Salesforce (BCC the Email-to-Salesforce address), the emails are NOT associated and displayed under the Activity History section of that record; nor in the Unresolved Items.
SPF, Sender ID, or DomainKeys.
For Salesforce to accept an email with this feature turned on, your Users’ email server has to support at least one of the following protocols: SPF, Sender ID, or Domain Keys.
When this feature is enabled, these protocols are used to verify the legitimacy of the email sender's server. If the server passes at least one of the protocols, then Salesforce processes the email.
After this change, try to reproduce the issue and confirm that it has been added to a Salesforce record or to the Unresolved Items queue.
Note: Engage your IT/Salesforce administrator team if you want to keep Advanced Email Security Settings enabled and reference the following contents:
000384459

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