Using the default MTA (Postfix), the following needs to be configured. I have tested authenticating to an Exchange 2010 server.

I am not really sure about the minimum software needed in CentOS 7 for this, but I did install the following in a minimum installation (postfix installed by default):

cyrus-sasl-plain
cyrus-sasl-lib

Create a credential file:

# cd /etc/postfix
# vi cr_info
[my.server.domain] theusername:andtheirpassword
# chmod 600 cr_info
# postmap hash:/etc/postfix/cr_info

Configure postfix for smarthost authentication:

# vi /etc/postfix/main.cf

# JGZ 4/27/2018
relayhost = [my.server.domain]
smtp_use_tls = yes
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/cr_info
smtp_sasl_security_options = noanonymous

Restart postfix:

# postfix reload