Okay, so I've got a situation where client's emails are automatically being filtered and delivered to SPAM folders for recipients with hotmail/yahoo/gmail/etc, which, as we know, the spam folder is usually never checked. Thus, some of my users are hoping for a fix.

I've applied SPF records to each of my mail servers and it seems that emails to @gmail.com and @hotmail/live.com are no longer being treated as SPAM. However, it seems Yahoo likes to flag any emails from my mail cluster as SPAM, regardless of the SPF records.

Is there anything else I can do to prevent this? I've applied SpamAssassin and BoxTrapper to the mail servers, so I'm not quite sure where to go from here.

Anyone shed some light for me?
Thanks!

It's an art finding out how to get email delivered correctly to a
given domain. Sometimes you can get information by telneting to
port 25 on a mail server. Sometimes you can get a response from
abuse@<the domain> or postmaster@<the domain>. Sometimes you can
search their website and find information.

Having good SPF records is a start, but most mail servers use
other methods instead of or in addition to SPF checks.