mutt/exim - how to rewrite sender-name (-f flag)

["" <ds@blizznet.at>]

Hi all!

I'm using exim (MTA) and mutt (MUA) and I'm able to send (external) emails directly from exim with:
exim -f username recipient@domain.at

I have to rewrite the sender-name (which is not the same as the from:-address) with "username" which is expected from my ISP.

So:
* How do I tell exim (/etc/exim.conf) to rewrite any sender name of a local user with "username" (I'm a single user on my laptop)? or
* How do I tell mutt to rewrite the sender-name (ie joe@myhostname) with "username" (set sendmail="/usr/sbin/exim -f username" ... in my .muttrc doesn't work ... maybe my old version of mutt (0.91) doesn't deliver flags to exim)?

TIA for any help/clue
Dieter