outgoing email server hostname and port

I have a mac mini and Spectrum as my internet provider. my email is old with twc - nyc.rr.com

for incoming and outgoing email - the hostname is twc.mail.com.

I research told me to change the outgoing port to 587 - which I did>

Mail still keeps giving me errors - unable to find account or password.!!

I am getting emails but theres recurrent errors - offline or enter your password!

I cannot reply or send out any email!!!! help:)