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FreelanceWizard's profile

Visitor

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3 Messages

Wed, Aug 13, 2014 8:00 AM

SMTP service issue: connection refused and 421 service unavailable

I've been using SMTP to send e-mail from systems outside of the Comcast network through Comcast's hosted Exchange for almost 3 years now without any issues. Until recently, I'd just aim the external system at the SMTP server address listed on the DNS page in my account (smtp.po1.comcast.net) on port 25, turn on SMTP authentication using the credentials of a service account mailbox I created in the web interface, and everything would work just fine.

 

However, I noticed recently (around 8/6) that these systems were unable to send e-mail. Digging into it, I noticed that the SMTP server address on the DNS information page had changed to smtp.w14b.comcast.net. After making the change, I noticed that the systems were still unable to send e-mail. I decided then to break out PuTTY and test a few things.

 

1. Port 25: smtp.w14b.comcast.net refuses connections on port 25.

2. Port 587: smtp.w14b.comcast.net does some weird things here. From some source IPs, the connection is refused outright. From other source IPs, I get as far as EHLO, but immediately get "421 Service unavailable; closing control channel" back from the server.

3. Port 465: smtp.w14b.comcast.net accepts the connection, but fails to respond to the SSL handshake, then drops the connection. (This one I had to verify using a mail client and Wireshark.)

 

smtp.po1.comcast.net exhibits similar behavior.

 

Could I get confirmation on whether this is a service outage on this new mail server or a policy change? If it's a service outage, is there any word on when it might be fixed?

Accepted Solution

Advocate

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1.4K Messages

8 y ago

Hello FreelanceWizard and welcome,

 

Please see my comments/response below. Thanks.

 

 

 

1. Port 25: smtp.w14b.comcast.net refuses connections on port 25.

 

Yes, Outgoing port 25 is now blocked by the Industry (including Comcast) due to one of the most recent Email Hacker Scams that took place.  So now Comcast always blocks port 25 for security reasons. 

 

2. Port 587: smtp.w14b.comcast.net does some weird things here. From some source IPs, the connection is refused outright. From other source IPs, I get as far as EHLO, but immediately get "421 Service unavailable; closing control channel" back from the server.

 

If you are running IMAP then you should be using incoming port 993 and outgoing port 587 and the encrypted setting should be SSL. However, if you are running intrinsic POP, then try using incoming port 995 and your outgoing port should be 587 for in-network or 465 for out-network.

 

3. Port 465: smtp.w14b.comcast.net accepts the connection, but fails to respond to the SSL handshake, then drops the connection. (This one I had to verify using a mail client and Wireshark.)

 

Port 465 is only used for Comcast emails that are out-network meaning they are on an email server not being hosted by Comcast.  It would be helpful if you could share your email suffix address like @your-domain.name

 

Hope this helps you out.

 

 

 

 

 

 

Visitor

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3 Messages

8 y ago

Inexplicably, it's working now without any setting changes; when I left it before I wrote the original post, I was using 587 without SSL, and now it's working when I verified the settings and tested it again. Curious.

 

It's always nice when a problem works itself out, right? 🙂

Advocate

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1.4K Messages

8 y ago

Well, if it just started working then it must have been an email server temporary outage that was fixed or rolled over.

 

Bottom line, I am glad that you are up and running.

 

Take care.