Fetchmail/Sendmail problem after installing FC2

[Colin Paul Adams]

After installing (from scratch, apart from /home directory) FC2, I can
no longer receive mails from a particular address. I used to receive
mails from him when I had FC1 installed.

The address concerned has an MX record - I can get a listing with dig
-t MX, but if I omit the -t MX record, then I get:

Truncated, retrying in TCP mode.

and then timed out - not servers could be found.

fetchmail/sendmail rejects his emails with:

maillog.1:Jun  7 23:53:45 colina sendmail[29693]: i57MiHN5029693: ruleset=check_mail, arg1=<neal at 3dsafety.com>, relay=localhost.localdomain [127.0.0.1], reject=451 4.1.8 Domain of sender address neal at 3dsafety.com does not resolve

So my questions are:

1) Is there a fix for this?
and if not,
2) Can I tell sendmail to always allow this particular address through?
-- 
Colin Paul Adams
Preston Lancashire