Email traffic referrer

Some affiliate programs allows email traffic only . For the last years big services like hotmail and yahoo were transferring the referrer. But since last year hotmail is longer shows the referrer and recently yahoo did the same. I?m worried that 99% of the traffic is coming without referrer, i.e. blank or direct.
There are plenty of reasons of eliminating the email referrer. Most of popular email services don?t transfer it. Moreover, people are using other mail clients and programs to check emails.
Did anyone had any issues with advertisers regarding this?