What Outgoing email address setting should be used for three email addresses on my devices?

I have three centurylink email addresses coming into each of my devices. The three INCOMING email settings have different user names and passwords. That setup works. The OUTGOING settings are not working for all email addresses. Does one email address OUTGOING setting have to be used for all? Or does each email address require their own settings for OUTGOING emails? The OUTGOING settings call for User Name and Password although the word “OPTIONAL” is shown. Do I put in the user name and passwords or not? Thanks. Bonnie