Getting rid of all first.last@domain contacts from your address book and replacing them with proper entries (or merging if that's possible). More on https://pawelniewiadomski.com/2016/06/08/cleaning-addressbook-with-swift-scripting/

address-book.swift

#!/usr/bin/env swift

import Cocoa
import AddressBook

var ab = ABAddressBook.sharedAddressBook()

func findByFirstAndLastName(firstName: String, lastName: String) -> [ABRecord] {
    let comparison: ABSearchConjunction = CFIndex(kABContainsSubStringCaseInsensitive.rawValue)
    
    let searchForEmptyLastName = ABPerson.searchElementForProperty(kABLastNameProperty, label: nil, key: nil, value: lastName, comparison: comparison)
    
    let searchForEmptyFirstName = ABPerson.searchElementForProperty(kABFirstNameProperty, label: nil, key: nil, value: firstName, comparison: comparison)
    
    let andComparison = ABSearchElement(forConjunction: CFIndex(kABSearchAnd.rawValue), children: [searchForEmptyLastName, searchForEmptyFirstName])
    
    return ab.recordsMatchingSearchElement(andComparison) as! [ABRecord]
}

func findWithoutNames() -> [ABRecord] {
    let comparison: ABSearchConjunction = CFIndex(kABContainsSubStringCaseInsensitive.rawValue)
    
    let searchForEmptyLastName = ABPerson.searchElementForProperty(kABLastNameProperty, label: nil, key: nil, value: "", comparison: comparison)
    
    let searchForEmptyFirstName = ABPerson.searchElementForProperty(kABFirstNameProperty, label: nil, key: nil, value: "", comparison: comparison)
    
    let andComparison = ABSearchElement(forConjunction: CFIndex(kABSearchAnd.rawValue), children: [searchForEmptyLastName, searchForEmptyFirstName])
    
    return ab.recordsMatchingSearchElement(andComparison) as! [ABRecord]
}

for person in findWithoutNames() {
    let emailsProperty = person.valueForProperty(kABEmailProperty) as! ABMultiValue?
    if let emails = emailsProperty {
        for i in 0 ..< emails.count() {
            let email = emails.valueAtIndex(i) as! String
            let name = email.characters.split("@")[0]
            if name.contains(".") {
                let parts = name.split(".")
                if parts.count == 2 {
                    let firstName = String(parts[0]).capitalizedString
                    let lastName = String(parts[1]).capitalizedString
                    let matching = findByFirstAndLastName(firstName, lastName: lastName)
                    
                    if matching.count > 0 {
                        for another in matching {
                            let anotherEmails = another.valueForProperty(kABEmailProperty)?.mutableCopy() ?? ABMutableMultiValue()
                            anotherEmails.addValue(email, withLabel: kABEmailWorkLabel)
                        }
                        ab.removeRecord(person)
                    } else {
                        print (firstName, lastName, email, matching.count)
                        
                        person.setValue(firstName, forProperty: kABFirstNameProperty)
                        person.setValue(lastName, forProperty: kABLastNameProperty)
                    }
                }
            }
        }
    }
}

ab.save()