I use a very low-tech approach. A spreadsheet (LibreOffice) with name, position, company and phone number in the leftmost columns and then a column for each form of contact. Copy and paste into the various apps and over-time the apps build their individual contact lists. People don't change their identities often enough for me to want to automate synchronization across the various apps.\

If you are contacting more than a hundred or so persons, then you are running bulk emails which is a different issue.