/ in MAIL FROM

H!

Yandex not allow / in MAIL FROM.
Our setup sometimes produce / in rewrited addresses:
from=<SRS0=9yTC74/9T2=XQ=...>
from=<SRS0=FgJ/Q+/dzw=XQ=...>
from=<SRS0=LsA7Oe/xqm=XQ=...>

I reduced hash-length and hash-minimum to default 4. But not sure will help it or not.
Is there a way to get rid of /?