The default SELinux configuration will block WordPress from sending emails. Using the check email plugin, error messages can be found in /var/log/audit/audit.log:

type=AVC msg=audit(1368370436.817:271444): avc:  denied  { search } for  pid=13875 comm="sendmail" name="postfix" dev=dm-0 ino=1179960 scontext=unconfined_u:system_r:httpd_t:s0 tcontext=system_u:object_r:postfix_spool_t:s0 tclass=dir

To overcome this, the SELinux boolean ‘httpd_can_sendmail’ must be set to on.

# getsebool -a | grep httpd_can_sendmail
httpd_can_sendmail --> off
# setsebool -P httpd_can_sendmail=on
# getsebool -a | grep httpd_can_sendmail
httpd_can_sendmail --> on

The -P flag is for the boolean setting to persist across reboots.