On Jan 9, 2006, at 3:29 PM, David Vallner wrote:
> Speaking of which, by mere coinkydink I needed that article right  
> now too. Yet my ISPs SMTP server doesn't seem to let me through;  
> does anyone know what are the common limitations that ISPs enforce  
> on e-mails sent via their SMTP servers? I'm wondering whether  
> setting my HELO domain to my webhost's as opposed to something that  
> looks like what the ISP might have given me could cause a failure  
> in the mail being deliverred.


Many ISPs block outbound TCP connections to port 25 (the SMTP port).
They require you to connect to the mail server provided by the ISP,
which will then deliver the mail outside the ISP's network.

Some ISPs have a procedure to lift the outbound port 25 filters for  
specific
customers.  You'll have to check with your ISP.

You can thank the spammers for this situation.  It is designed to  
provide
a mechanism for auditing outgoing email such that spam sources can be  
identified
and shutdown before they cause the ISP to be put on various  
blacklists as a source
of spam.   If your address block gets put on such a list it can have  
a serious
operational impact (i.e. email to/from your customers stops flowing)  
so ISP's
have to be aggressive about identifying and eliminating sources of SPAM.

Gary Wright