# mail '[fax: bh@9999494178]'
[fax:bh@9999494178] contains invalid character '['


#mail "[fax: bh@9999494178]"
[fax:bh@9999494178] contains invalid character '['


Seems you may have problems other than with a SPACE with this idea........ since I'm not sure how you are aliasing the fax service (the TO ADDR), I can't help further, sorry.

From man.....



mail [-BFintv~] [-s subject] [-a attachment ] [-c cc-addr] [-b bcc-addr] [-r from-addr] [-h hops] to-addr ...