Contacts That Have Email Forwarding Set Up Might Respond to Emails from a Different Address 

It's common for contacts to have multiple email aliases or domains, each set up to forward to the other. For example, if you email a contact at testymctesterson@domain.com, they may respond back to you from testymctesterson@seconddomain.com. Or perhaps they have changed their name and went from testymctesterson@domain.com to tisthebesttest@domain.com.

When this happens, Apollo is able to recognize that the response is part of the same email thread and so will log the reply as an activity on the original contact's profile.

However, the 'new' email will not yet exist as a contact in your app, and so searching for them won't bring you to the existing account, but instead will prompt you to create a new contact.

Depending on what works best for your workflow, you can either create the "new" contact in your app, or update the original contact with the new email.

Important: If you have Salesforce integrated with your Apollo app, there is an option to push Emails even if the sender or recipient doesn't yet exist as a Contact. However, this option may create new Contacts in Salesforce so should be used with caution.