Activity › Forums › Salesforce® Discussions › For which data type we can enable external id? Salesforce® Discussions For which data type we can enable external id? Posted by Prachi on August 31, 2018 at 1:40 PM For which data type we can enable external id? Anurag algoworks replied 7 years, 9 months ago 2 Members · 1 Reply 1 Reply Anurag algoworks Member August 31, 2018 at 2:18 PM Hi Prachi, A custom field can be marked as an external ID to identify the primary keys of the legacy system (outside Salesforce). Text, number, e-mail, and auto-number fields can be flagged as external IDs. Log In to reply. Public All Members My Connections Only Me PublicAll MembersMy ConnectionsOnly Me Public All Members My Connections Only Me