Slightly OT:Can Sendmail or Postfix do this?

[Steve Mason]

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I'm currently running  MailScanner, SpamAssassin, and Postfix on a
Fedora Core 2 box, and all is great, mostly...

I have my own domain, and I'm also using Fetchmail to pop some other
externally hosted accounts. Users have IMAP clients and get their mail
from the Fedora box. Depending on the account, they SMTP back through
the Fedora box, or through the ISP mail server

The problem is that my Fedora box is on a dynamic (doesn't change often
though) IP address, and more and more hosts (including the Mailscanner
list server) don't want to talk to my mail server.
My domain's  DNS is hosted externally, with the MX record pointing to my
dynamic IP. I suspect that some mail servers either don't like the fact
that my server is in a dynamic IP range, or that the reverse lookups
don't match my domain name.
I don't mind hosting my domain externally (I do for web content) but I'd
still like to run a mail server here, with MailScanner.

So what I'd like to do is --  host my own domain mail externally, and
use Fetchmail to pop it to the Fedora box. That part is easy.
I'd also like outbound mail (from the mail clients , mostly Thunderbird
users) to send via my Fedora box, and relay to the different external
mail servers.

Can either Postfix, or Sendmail relay outgoing SMTP to different hosts
based on the from: field?
For example, my computer runs Thunderbird, and I have several mail
accounts.  me at mydomain.com me at myispdomain.ca and me at 3rdpartymail.com
Depending on what account I'm sending from, I'd like my Fedora box to
send outbound mail either to  externalmailserver at mydomain.com or
mail.myisp.ca or smtp.3rdpartymail.com

If it were just one domain/server smarthost and masquerade as would
likely do it? But can I do this with the multiple domains/servers?

Thanks,

Steve

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