Weddingbee boards

For the RSVP response envelopes I was originally planning on using a custom stamp I ordered and then embossing it.  However, after researching, it appears that this won't work (because it's embossed and also because the stamp has our names in the middle, street address on top, and city and state below the names). 

I have the L Letterpress machine and used it for my STDs and will be using it for my invitations, so I figured maybe I could just use it on the envelopes as well.  This might be a good alternative to handwriting out the addresses or printing (from the computer) the addresses.  Has anyone letterpressed their address onto envelopes? Also, do you think there would be any issues with the post office (maybe I should use a certain color ink?  I will be sure to have our address in the traditional order and in a legibile font)?  Thanks!