I recently noticed some emails going missing, this was due to the params on the emails trying to assign the sender as a domain outside Dreamhost (I suspect due to SPF protected domains mainly, because forging a nonexistant domain is fine, example.com will work with softfail).
This seems perfectly acceptable, but it seems like a new issue - I'm not sure the emails are even getting outside the DH network and it is shown as a successful send.
This PHP will work. (replace youremail and yourdomain)
echo(mail('firstname.lastname@example.org','Your Domain params','message','Return-Path: email@example.com\nFrom: testxyzxcyzyxzy <firstname.lastname@example.org>\n','-oi -f email@example.com'));
This PHP will not arrive. (replace youremail)
echo(mail('firstname.lastname@example.org','Hotmail params','message','Return-Path: email@example.com\nFrom: testxyzxcyzyxzy <firstname.lastname@example.org>\n','-oi -f email@example.com'));
Is this a new issue after DH changed their email policies/code ? or is it more likely just the SPF settings of the other domains causing "correct" SPF behaviour?
It looks like it is impossible to use -f unless you are 100% sure the domain is allowed to be used by you - so just don't do it... Some CMS do use these params because they use phpmail.php, so it is possible to lose emails if you are using a badly coded addon or for example, you assume you can use any email address in some newsletter sending configurations etc...