If you are using SQLite (quick start default) then you’ll need to open the file a client and delete entry in the strapi_administrators table (DBeaver community is a free, cross platform client that works well on any SQL database)
For others the same applies but need a client and the information to connect to the database server.
Email is likely failing (default it’s setup to use sendmail from your local machine) due to most ISPs blocking outbound port 25 to prevent email spam.