sb5309@yahoo.com writes:

> At my office:
>
> OK (out-going mail): telnet servername 25
> OK: telnet servername 110
>
> At my client's office:
>
> No: telnet servername 25
> OK: telnet servername 110
>
> On advise of the web host, at client office change port 25 to 587:
>
> OK: telnet servername 587
>
>
> Question: Why is this so ?

I work at a web host, we tell people to change to 587
in cases where their ISP blocks port 25 connections attempting
to leave their network, i.e. they are trying to stop spammers.


--
John
__________________________________________________ _________________
John Murtari Software Workshop Inc.
jmurtari@following domain 315.635-1968(x-211) "TheBook.Com" (TM)
http://thebook.com/

On Wed, 23 Apr 2008 12:40:10 -0400, John Murtari wrote:

> I work at a web host, we tell people to change to 587 in cases where
> their ISP blocks port 25 connections attempting to leave their network,
> i.e. they are trying to stop spammers.

I don't know the history, but somewhere along the way 587 became the
standard "email submission" port. The idea is that this is distinct from
"email transfer", the latter being server-server and the former being
client-server.

This permits different rules (or even different softwares!) to be applied
to the different ports. Incoming traffic on port 25 must be to a domain
handled by that server, for example, while incoming traffic on port 587
must be authenticated.

At least some SMTP servers (ie. sendmail) can be configured to handle
"local domain or authenticated" on a single port, which is where I suffer
from a bit of ignorance: I don't know why the desire for different ports
arose. Perhaps to run different softwares for the different audiences w/
o wasting IPv4 space?

- Andrew

sb5309@yahoo.com writes:

> At my office:
>
> OK (out-going mail): telnet servername 25
> OK: telnet servername 110
>
> At my client's office:
>
> No: telnet servername 25
> OK: telnet servername 110
>
> On advise of the web host, at client office change port 25 to 587:
>
> OK: telnet servername 587
Earthlink ISP advises the same for configuring email clients. All I
know is that it works.

--
Allan