port question

[Tony Alfrey]

Bruce Marshall wrote:
> On Sunday 23 August 2009, Tony Alfrey wrote:
>> plonking Bob.  Yes, that is what I've concluded.
>> I'm thinking it's not a block of Port 25, 'cause Tony's incoming mail
>> server (earthlink) already blocks Port 25 and Tony gets mail from Alice
>> and Bob.
> 
> I think you're getting confused here....

Certainly a distinct possibility.

>  Earthlink may block YOU from running 
> a mail server....  and they can do that by not letting any port 25 calls go to 
> your machine while connected to earthlink.   Same might be true on port 80 to 
> prevent you from running a web site (server).

Ah!  What sets the port?  If I send mail with my mail client, does my 
mail client set the port on the packets I send?  If I set port 25, 
earthlink may block my mail packets.  Is this correct?

> 
> But earthlink can't really block its own port 25....    cuz no one would get 
> any emails through earthlink if they did.

I read that "earthlink blocks port 25".  My understanding is that this 
means that the TCP/IP packets themselves have the port set within the 
header of the packets and that this is what determines if the received 
packet is blocked.  Is that correct?


-- 
Tony Alfrey
tonyalfrey at earthlink.net
"I'd Rather Be Sailing"