Verizon and Comcast email challenges

Gordon Messmer yinyang at
Wed Jul 21 06:09:21 UTC 2010

On 07/20/2010 02:39 PM, Max Pyziur wrote:
> Recently (over the last six months?), Verizon has blocked smtp requests on
> port 25 to our mail server hosted on our machine ( It seems
> that this isn't just our box, but a policy that Verizon has implemented
> widely, forcing Verizon patrons to use someuser at to send
> outbound email, or use a different port (587?).

That's fairly common for residential service.  More ISPs are doing so, 
and it's good practice for limiting spam.  If you run an SMTP server, 
ask your ISP for a business-class account.  You'll pay more, but you 
won't have filtered access.  I don't think there's any other way for you 
to run an MX for your domain on one of their lines.

If you want to allow users to send email through your server, you should 
definitely run an SMTP server on port 587.  It should require SMTP AUTH 
for relay privileges.  You will probably need to configure your server 
to use Verizon's SMTP servers as "smart hosts" to relay your mail.

> More recently, recipients with cannot receive emails from our
> hosted domain names. As yet, I only have bare knowledge with the
> indication that the Verizon problem rests with finding an answer at the
> following website:
> Sender Policy Framework

That's possible.  You did publish an SPF+ record for  What 
leads you to believe that this is the source of the problem?

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