Position the multiple return addresses side by side, or directly beneath one another. Start in the upper left-hand corner of the envelope. The mailing address will be written on the lower center or slightly right of center on the front of the envelope. Keep the handwriting neat and legible, and separate from the mailing address.
Use small print to fit in all the necessary information without making the address difficult to read. This is especially vital when writing multiple return addresses on small envelopes. You may also need to use initials for first names and abbreviations where appropriate to save space on the outside of the envelope.
Keep the distinction between the mailing address and the return addresses clear. Include sufficient white space between addresses or draw a box around the return addresses to create a visual separation. You may go so far as to write "TO:" in large letters before the mailing address so the postal service delivering the envelope does not get confused about the intended destination.
Write the remaining return addresses on the back of the envelope. This will help make the distinction between mailing address and return addresses even more clear. Be sure to stamp the side with the actual mailing address so there is less confusion at the post office.