In article <44e5602e@news.ish.de>, Uwe Behle <posting2@df3du.mine.nu> writes:
>devon_banks@comcast.net schrieb:
>> Why are you sending your email via your ISP when you have an SMTP
>> server?
>> I ask because I recently got the same email message about security from
>> my ISP.
>> But I currently have my internal email clients using my sendmail server
>> as the SMTP server and the clients are pulling POP3 from the ISP and my
>> internal POP3 server.
>
>Because, for fear of spam, more and more ISPs reject mail if you are not
>in their accepted IP-address range.
>
>Uwe

Lots of mail servers check against lists such as
MAPS DUL (http://www.mail-abuse.com/enduserinfo_dul.html) and
SORBS DUHL (http://www.us.sorbs.net/faq/dul.shtml)

which list ISP's dynamically assigned address ranges but not the ISP's own
central mailservers.

Hence if you set up your own mail server using the broadband address provided
by your ISP and try to send mail out directly rather than through your ISP's
mail server you will probably find quite a lot of your mail rejected.

(A number of ISPs also block outgoing port 25 connections which effectively
stops direct sending of mail. To overcome it you either have to send through
the ISP's mail server or through another server with which you have made special
arrangements so that you can send using a different port).


David Webb
Security team leader
CCSS
Middlesex University