I usually just use a 6x9 envelope - not padded. What about checking at a dollar store? They often sell greeting card envelopes that are left over - and they are usually larger - packs of about 25 bundled together. I fold my blocks and wrap them in plastic wrap or a baggie before putting them in the envelope. I think they have always arrived safely.
Sue

Like Sue, I fold the block into quarters and put it in a quart-sized baggie. Then into a manila envelope. It's usually about a $1.40 or so to mail.

I buy the largest greeting cards I can find at Dollartree at 2/$1. I fold the block to fit the card, wrap it in Glad Press and Seal and mail it as a greeting card. It is the cheapest was to mail it from Canada.

Mary

I use manilla 6x9 envelopes as well. That size is under the limit for first class letter rate and is mailed as a letter so usually costs only 2oz which is one regular stamp plus the 20 cents second ounce. I haven't had one go over 2 ounces yet.

I usually send 3 months blocks at once and 3 per month so they don't fit in a small envelope. But the Dec. block is ready to go so I will use the card envelope idea.
Theresa

Thanks for all the great suggestions. DO NOT procrastinate is my new "motto for the lotto". I didn't get it sent out until this afternoon, so had to send it priority mail! Silly too since I had them in the car for two days.

Most lotto blocks are received in unpadded 6x9s, and all arrive OK. Large greeting cards work fine too but don't get one so large you have to pay extra postage. Square envelopes, for some reason, cost more. I'm sure it has to do with post office processing equipment.