On May 7, 2017, an error occurred which changed the email addresses of a small number of HubSpot contacts. The HubSpot Engineering team has identified and fixed this issue.
In the majority of cases, email addresses were converted to lowercase. For example PEETER@HUBSPOT.COM would have been converted to firstname.lastname@example.org.
However, there was a small number of contacts that had their email addresses changed to a new value. This affected contacts that had been previously merged and had their email address updated after that merge. On May 9, 2017, the Engineering team restored the previous email property values for these contacts.
How will I know if a contact was impacted by this?
When looking at a contact's property history, you'll see an update to the Email property with the change source of Migration between May 7, 2017 and May 9, 2017.