Hello,
Is there any way where I can change the "from" address in the maillogs without
changing the envelop sender.

We have email users using smtp-auth with multiple email accounts but authenticating against single user account.So whenever a user sends mails through our server from any one of his multiple mail accounts,I want to be able to change the "From address" to the user he is authenticating against instead of the "from address" which he supplies, in the maillogs.

We have mimedefang running on our system,I tried using things like change_envelope_sender functions,but it only changed the envelope sender and did'nt change anything in the maillogs.

Any help in this regards is much appreciated.

The mail logs typically reflect the actual smtp mail being sent through the system, you may be able to turn up logging level and turn on verbosity and get that information however.