How to: Validate an e-mail address in a SharePoint text field – validation rule

In list settings change the column’s validation settings to:

=(LEN(LEFT([Attendees (external)],FIND(“@”,[Attendees (external)])-1))>=1)+(LEN(RIGHT([Attendees (external)],LEN([Attendees (external)])-FIND(“.”,[Attendees (external)],FIND(“@”,[Attendees (external)]))))>=1)+(LEN(MID([Attendees (external)],FIND(“@”,[Attendees (external)])+1,FIND(“.”,[Attendees (external)],FIND(“@”,[Attendees (external)]))-FIND(“@”,[Attendees (external)])-1))>=1)+(ISERROR(FIND(” “,[Attendees (external)]))=TRUE)=4