Dynamic 'myhostname'

[Mick]

Hi,

I'm trialling DMARC to two of my domains.  On checking the results when 
posting from the secondary domain I receive 'SPF Domain Alignment Result 
= FAIL'. I think this is because postfix always says HELO with the 
primary domain name, which is obviously different to the secondary.  Is 
there a way to rewrite the message envelope to say HELO using the same 
domain used in the from field?

Thanks,

Mick.