A wild arcane familiar suddenly appears

I used to play as arcane but recently switched to frost because I was doing horrible dps even after the recent buff… so I’m not too familiar with this spec. I noticed that sometimes an arcane familiar appears next to me, and he has an envelope in his hands. Who is this little fella? What’s the deal with the envelope?

I assume it’s your trinket, the 'mailemental".

Mystery solved. This is what you get when you rotate characters a lot.
I was secretly hoping it was a profession quest or some other hidden achievement.