A very useful thing to do is to create an NK2 file for autocomplete in outlook from sent items. From this post:

https://www.experts-exchange.com/questions/28243809/Nuild-NK2-file-from-sent-Item.html

The idea is to export the email with only the from:address field to a csv. Then use Excel to deduplicate (under data) and then copy the entire field as a new message. Once copied, they will all be in autocomplete.