hylafax faxcover command has got -M option to include recipient Email address but avantfax faxcover.php doesn't.
attached is the proposed patch
proposed faxcover.php patch
There is no -M option in HylaFAX 4.4 or HylaFAX EE.
But there is -M option in Hylafax+ since version 5.1.11 (a year ago).
So I think it could be of general interest supporting this feature, even because Hylafax 4.4 does not produce a new release since 21 dec 2007. IMHO the community development are migrating to Hylafax+...