outgoing email no longer working

I'm sorry. We've tried typing in the user name and the password in those fields instead of checking the use same logon as incoming server option, and it rejects the login information, even though it's the correct information for the account - i.e., the correct username and the correct password. Nothing we do seems to change this. We simply cannot log on to the smtp server through a client, even when we've changed the port settings to those cox advises we use as of Jan. 28, 2018. We don't have any problem using the webmail and may well just go that route on all devices. 

In case I haven't been clear, my wife's account is set up as an imap account with logon credentials that work, but when we use the same logon credentials to connect with the smtp server to send mail, it rejects those logon credentials. We have tried checking and unchecking every option and tested them all. None works. Thanks.