Here is my advice regarding any guest communication regarding a postponement: 

1. Keep it brief.  You don’t need to explain everything.  
2. Give the new date.  If you don’t have a new date, that’s ok – say you’ll let them know when you have one.  It’s ok for things to be TBD if you are uncertain of the new plan.
3. If you have a new date, give a link for online RSVPs.  You don’t need to mail out an entirely new invitation suite unless you want to.  
4. If you have new room block information, put it on your website (and mention it in the card or email).  
5. End on the positive – you are still in love and you are still going to get married!​

If you want some free options that you can personalize, our friends at Wedding Chicks have some great options!

Here is my favorite.

This one is cute too.

Just remember: Communication Is Key.  Your guests have invested their own funds into travel, taking vacation time, reserving time in their busy schedules, etc. – so you want to be respectful and communicate the updates quickly and efficiently so they can change their plans as needed.​