If you're going to store in an envelope, at least put it in a baggie first.

I store my herb in glass jars. Keeps it fresh and delicious for weeks on end. You just have to be careful to make sure the weed isn't too wet, otherwise mold is at risk. That's why if my buds are a little dankish, I leave them out for about 12hrs to fully dry. I prefer my buds really dry. No risk of mold, and no worries.

Around here, some people store cannabis inside of envelopes because if they get pulled over, if the officer sees and envelope, he can't open it, as long as you say it is mail for the mailbox. They need a search warrent to open them, as long as there isn't an obvious reason that you're hiding illegal drugs in the envelope.

One of my guys used to do it all the time with small amounts. Small amounts I mean no more than a 1/4. A bulging envelope is too obvious, but for gram dealers, it's perfect.