Hello!

I will be moving out of Zurich for few months (6-8 months) due to an assignment in another country after which I will return to Zurich. As it may not help me to maintain an apartment during this period, I will be vacating it as well. Any suggestions on how I can still maintain a postal address in Zurich ( without an apartment/residence) for correspondence ?

Check with the landlord, if it is allowed to sublet your appartment ?
Keep the address,saves a lot of problems.

I think you'll want to consider more than just the postal address. Your profile says you're neither Swiss nor an EU citizen. As such you will probably want to request to put your permit on hold while you're abroad so that you can return when that assignment is done. Otherwise when you de-register, that's it and the employer has to again go through the non-EU process to hire you in order for you to return.