Epistolary Poetry

So this summer, I went to a camp that had numerous workshops about poetry and wiritng in general. One of the things I was introduced to is something called epistolary poetry. This is letter writing in poetry, in  a sense. I've read multiple epistolary poems and written some too, without knowing their proper (sub)genre. 

I must warn you, I am now obsessed with epistolary poetry, so when you view the sudden onslaught of the stuff, don't say I didn't warn you. :)