I have recently discovered that megapathdsl.com checks all mail (inbound and
outbound) for SPF. They then apply the Received-spf header. They only
reject inbound failures. Now one might assume that receivers would ignore
Received-SPF headers applied by previous MTAs. That is not always correct.
I had one case of a mail rejected and another case of a reply letting me
know that my messages were going into an SPF Fail folder.
I've discussed this with Megapath support and they aren't changing how they
do their SPF checking, so if you are a Megapathdsl customer and you send via
their MTA, then you might want to add your client IP address to your SPF
record so that you don't have mail with a SPF Fail received header in it.
That's what I've done.
Scott Kitterman