Need WordPress to send email, but you’re on Comcast?

Sending mail with Comcast as your ISP – this is on CentOS 7.2.

Install:
# yum install cyrus-sasl{,-plain}

Edit /etc/postfix/main.cf and insert the following below the other ‘relayhost’ references:
relayhost = [smtp.comcast.net]:587
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/smtp_password
smtp_sasl_security_options =

Note: smtp_sasl_security_options = … is intentionally blank.

Edit:
/etc/postfix/smtp_password and insert:
[smtp.comcast.net]:587
username@comcast.net:password

Lock down the perms:
# chmod 600 /etc/postfix/smtp_password

Run:
postmap hash:/etc/postfix/smtp_password

Create a localhost-rewrite rule. This must be done, or else the Comcast SMTP server will reject your mail as coming from an invalid domain. Insert the following into:
/etc/postfix/sender_rewrite:
/^([^@]*)@.*$/ $1@<
your_domain_here>.com

Allow SELinux to accept apache’s access to send mail:
# setsebool -P httpd_can_sendmail 1

Restart postfix:
# systemctl restart postfix

Test. If it fails, tail /var/log/maillog!

** NEW INFO **
I had some troubles with this (mail still showing root@localhost in the maillog) – and here were a few more steps, if that doesn’t completely work.

vi /etc/postfix/sender_canonical

… and insert the following, to make “root” appear to be the “wordpressuser” on outbound mail. This should have been rewritten by the rule up above, but it wasn’t doing it.

root wordpressuser@yourdomain.com

Create /etc/postfix/sender_canonical.db file
postmap hash:/etc/postfix/sender_canonical

Add sender_canonical variable to /etc/postfix/main.cf
postconf -e "sender_canonical_maps=hash:/etc/postfix/sender_canonical"

Restart postfix:
# systemctl restart postfix