MX records check and SMTP greeting

I know I put two problems here but thought better to, "kill two birds with one stone".

Errors are from DNSstuff.com

Not sure how to do this one first warning or if it really needs to be fixed.
MX records check:
Only one MX record exists within the zone. This is ok, but it is a better practice to have at least two mail servers operating on a domain, to ensure more reliable mail deliverability. The MX record provided is:

preference = 10 mail.redtalkers.net. [23.31.67.21]

Now this I have looked through other posting and I just can't get a handle on it, maybe I am looking to hard at it or over processing it. But with this one please baby steps.
SMTP greeting
Malformed greeting or no A records found matching banner text for following servers, and banner is not an address literal. RFC5321 requires one or the other (should not be a CNAME). If this is not set correctly, some mail platforms will reject or delay mail from you, and can cause hard to diagnose issues with deliverability. Mailserver details:

23.31.67.21 | WARNING: The hostname in the SMTP greeting does not match the reverse DNS (PTR) record for your mail server. This probably won't cause any harm, but may be a technical violation of RFC5321

 

as far as MX records check, this is in fact what I thought.

This is what I changed in the postfix.conf from what I am understanding from you.

I also have redtalkers.com, redtalkers.org and windsofchangepcs.com. Would I in fact add those also? As far as my ISP goes, comcast will only add redtalkers.net they will not add mail.redtalkers.net

I am not finding /etc/mailname. where in centos 6.5 is this please?

# INTERNET HOST AND DOMAIN NAMES
#
# The myhostname parameter specifies the internet hostname of this
# mail system. The default is to use the fully-qualified domain name
# from gethostname(). $myhostname is used as a default value for many
# other configuration parameters.
#
myhostname = mail.redtalkers.net
#myhostname = virtual.domain.tld

# The mydomain parameter specifies the local internet domain name.
# The default is to use $myhostname minus the first component.
# $mydomain is used as a default value for many other configuration
# parameters.
#
mydomain = redtalkers.net

# Specify a list of host or domain names, /file/name or type:table
# patterns, separated by commas and/or whitespace. A /file/name
# pattern is replaced by its contents; a type:table is matched when
# a name matches a lookup key (the right-hand side is ignored).
# Continue long lines by starting the next line with whitespace.
#
# See also below, section "REJECTING MAIL FOR UNKNOWN LOCAL USERS".
#
mydestination = server1.redtalkers.net,mail.redtalkers.net, localhost, localhost.localdomain
#mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
#mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain,
# mail.$mydomain, www.$mydomain, ftp.$mydomain

 

ok still didn't work. I am going to call Comcast again and talk to another tech. I think they should be able to do it. Want to say how I feel personal but will not about comcast.

 

ok went to mxtoolbox.com and it says everything is fine. go figure.

 

ok called up comcast and they changed it to mail.redtalkers.net.

Would I need to change this at all?
# The smtpd_banner parameter specifies the text that follows the 220
# code in the SMTP server's greeting banner. Some people like to see
# the mail version advertised. By default, Postfix shows no version.
#
# You MUST specify $myhostname at the start of the text. That is an
# RFC requirement. Postfix itself does not care.
#
#smtpd_banner = $myhostname ESMTP $mail_name
#smtpd_banner = $myhostname ESMTP $mail_name ($mail_version)

 

Ok so as far as I am seeing this issue is resolved. I will have one more issue and that is it.