Re: Best Outgoing Mail, Via DNS or ISP SMTP?
- From: "spm" <nospam@xxxxxxxxxxxxxxxxxx>
- Date: Mon, 31 Jul 2006 11:10:08 -0700
Daren wrote:
I use the POP Manager to receive mail as my ISP (BT) scans everything
for viruses, so I get a nice big fat comfort zone.
But which is best... To send mail via the ISP or via DNS and if the
answer is DNS can anybody tell me why?
*In principle* it is better to route directly via DNS, for these
reasons:
- Routing via your ISP using POP3/SMTP has the inherent delays caused
by the 15-minute Exchange send/receive cycle (and reducing this below
15 mins is not advisable). There are no such delays with direct routing.
- If you are using global (i.e., multi-user) POP3 mailboxes at your
ISP, then BCC-addressed mails cannot be routed to your users by
Exchange (this does not apply if you have individual user POP3
mailboxes, though).
- Routing via your ISP can cause your emails to be blocked by other
MTAs, since the headers of your emails will reveal your server rather
than your ISP as the origin, while only your ISP's servers will have MX
records. Some receiving MTAs will consider this spam-like behaviour and
act accordingly.
However, routing direct via DNS does require you to get all your ducks
in a row, incl. MX records, rDNS (PTR) records, and SMTP open inbound.
Unless you can sort *all* of these, stick with POP3/SMTP via your ISP.
For instance, we surveyed a number UK ISPs recently when we changed our
broadband provider, and BT (who you say you use) said they would not
open SMTP for us unless we hosted our web sites with them.
Some other issues which may be of relevance...
- You make a point of saying that your ISP scans all your emails for
viruses. Does this mean that you have no A/V scanning on your SBS?
Assuming you do have, this isn't an issue.
- Exchange's IMF + Connection filtering does a competent job of
filtering UCE (spam) - though in our case, we do find the need to
supplement it with client-based 3rd party spam filtering. That said, a
peek at Exchange 2007 suggests there are important improvements on the
way in this respect...
--
Regards,
Steve.
.
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