Sending Mail From Comcast Was: Sendmail Not Working

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There are a few situations here.

1. You are a business customer with a static IP, and are entitled to send/receive SMTP by your ISP (Comcast)

2. You are a business/residential customer who is allowed to send (not likely allowed to receive) SMTP and you have a domain elsewhere to receive replies to your email

3. You are a business/residential customer who is NOT allowed to send SMTP except for your ISP (Comcast) provided email.

Only you would know which on for sure is you, but it is very likely #3.

The advice provided previously is for case #1 – contact Comcast and inform them that your contracted services are not working because of …. and you will need to beable to work with them on testing and suggesting fixes. They have a dedicated support phone number (which they provided you if you are actually a #1 type customer – e.g. gigabit pro, metro Ethernet, etc.)

In case you are a #2 or #3 type customer, you may want to use a smart host configuration – e.g. define(‘SMART_HOST’,'[smtp.comcast.net]’) . For postfix, use relayhost = [smtp.comcast.net] .

Now when you send mail to that relay it will relay it. This is provided you are entitled to have your email relayed – contact Xfinity customer service for help there.

If using this relay does not work, please post the exchange starting with the HELO (check your maillog or do it by hand with telnet).

15 thoughts on - Sending Mail From Comcast Was: Sendmail Not Working

  • Looks like the sendmail service isn’t running. Maybe it not starting because of a syntax errors?

    I’d probably not use send mail in the first place. Postfix is the default, recommended MTA in CentOS 7, and its less likely to have mysterious syntax errors and easier to understand configuration syntax. (Sendmail’s config language is so complex that most people just use M4 and “compile” it into the sendmail.cf)

    —
    Jonathan Billings

  • Sigh – bad examples for you…. undo if you can.

    Postfix provides the “sendmail” utility.

    # rpm -qf `which sendmail`
    postfix-2.10.1-7.el7.x86_64

    What does /var/log/maillog say ?

  • I get this:

    # rpm -qf `which sendmail`
    postfix-2.10.1-7.el7.x86_64
    sendmail-8.14.7-5.el7.x86_64

  • yum erase sendmail # undo what you did before… yum reinstall postfix # just in case it is messed up rpm -V postfix # lets verify if postfix is ok systemctl enable postfix # start on boot systemctl start postfix # start it now systemctl status postfix # see the status

    # setup Xfinity / Comcast SMTP relay ISP
    edit /etc/postfix/main.cf around line 315
    add
    relayhost = [smtp.comcast.net]

    systemctl restart postfix # restart to make changes effective systemctl status postfix # check status

    echo “Subject: sendmail test4” | sendmail your_xfinity_email@comcast.com # if this works, then test outside email

    echo “Subject: sendmail test4” | sendmail kevink@psalm19pix.com # does it get there?

  • OK, I’ve fired up a new VM, new CentOS 7 install, now I get this:

    # rpm -qf `which sendmail`
    postfix-2.10.1-7.el7.x86_64

    Can you point me to how to set this up properly? Note that I won the psalm19pix.com domain, it’s hosted at fastmail.com, and as far as I know requires SSL. Can I setup sendmail to use this as it’s SMPT connection?

    Thanks again…

  • See other thread/reply.

    No idea what all of that means. Contact support at fastmail.com? I am only helping with you sending mail from Comcast ISP.

  • my relay will be SMTP.fastmail.com and it requires authentication and SSL, are there added settings in main.cf that will allow this?

    Thanks

  • What port is that delivering to — that doesn’t sound like port 25, which is the default that an MTA delivers to.

    The postfix list may be a better place to ask these configuration questions. The general expectation there is that one has spent time going through the documentation.

  • Yes. You’ll want to use your favorite search engine to look up “CentOS postfix relayhost sasl”. Ignore any of the wiki.CentOS.org <http://wiki.CentOS.org/> links, they’re so out of date its embarrassing. (for example, the HowTos/postfix_sasl_relayhost wiki page tells you to use stunnel and an init service downloaded from a bugzilla post!)

    The important thing is you’ll set up SMTP_sasl_password_maps to point to a file that has your username and password so it can authenticate against SMTP.fastmail.com:587 <http://smtp.fastmail.com:587/>.

    You’ll have to make sure it goes to port 587 — traffic from Comcast customers to external port 25 is blocked.

    —
    Jonathan Billings

  • No, you are using Comcast / Xfininty per your IP address 50.243.150.81.

    Please follow the instuctions.

  • https://wiki.CentOS.org/HowTos/postfix_sasl_relayhost <https://wiki.CentOS.org/HowTos/postfix_sasl_relayhost>

    I might have complained too loudly about the wiki site, so now it has somewhat more accurate information. Please give feedback if it doesn’t work for you.

    These changes won’t remove your IP from the spamhaus DNSBL though — that’s something between your ISP and spamhaus. If you continue to get blocked I suggest you open up a case with your ISP because one of their IPs is being blacklisted and it is preventing you from sending email through their SMTP relay.

    —
    Jonathan Billings