How do I make sure inbound emails are being tracked in accounts?

Do you use Google or Office 365? Either way it's pretty simple to configure natively - SF support can assist if you have any questions. However there is a limitation on data retention for this native integration in Salesforce. We opted to build a custom Apex class that received and processed incoming emails and created task records with the lead/account based on specific criteria. We then created a DLP rule in Google to forward all incoming emails to this address. We can still batch delete old records if we ever need the space, but this works well for us.