[ On Thursday, March 14, 2002 at 15:59:58 (-0500), Dean Brooks wrote: ]
> Subject: Re: [Exim] HELO syntax checking in Exim 4
>
> The reality is that a large number of sites appear to use underscores
> in the element portion of a domain in helo responses, and we can't run
> a mail server in a vacuum - it has to operate in a real-world
> environment.
>
> The ultimate concern is that by rejecting underscores, we will be
> rejecting valid mail.
Ultimately by rejecting any connections with any kind of syntax error in
the HELO/EHLO parameter will result in rejecting valid e-mail.
Make up your mind -- do you want to risk it or not? Do you want to
enforce the requirements placed on the client-SMTP by the RFCs or not?
From what I've seen over the past umpteen years the number of legitimate
MTAs with underscores in their names, while growing, isn't all that much
different than the number with other forms of breakage. You should
either block them all, or none. Blocking only some of them leaves you
on very shaky ground w.r.t. explaining your rationale.
> In 2 hours of running Exim4 in production
> today, we blocked about 35 messages because of this. If we had
> let it run, we would have most certainly generated customer service
> calls within a day or two with people wanting to know why their
> email was being rejected.
The answer is pretty simple: "The system and/or software used by the
sender is broken. Our system was recently upgraded to protect itself
from that kind of breakage. If your correspondent wishes to send e-mail
to you then they will have to convince their ISP/sys-admin/whatever to
fix the software at their end."
If you really want to cater to a bunch of ignorant and obnoxious users
then you'll have to give up on enforcing any rules and just let them
have it all no matter what's broken. Unfortunately the ISP business is
so unprofitable these days that it's hard to tell the annoying users to
go elsewhere as doing so cuts even harder into your bottom line than
simply catering to them and wasting support and service costs on keeping
them as paying customers. In the early days it was easy for an ISP to
convince all the high-overhead customers to go drag down the competition.
--
Greg A. Woods
+1 416 218-0098; <gwoods@???>; <g.a.woods@???>; <woods@???>
Planix, Inc. <woods@???>; VE3TCP; Secrets of the Weird <woods@???>
