A question

I got an email last night that read

"How is 'Merry meet' and 'Blessed be' used?

Are these greetings to be used in certain curcumstances or like you say hello?
If in curcumstances please feel free to elaborate."

Myself, I have heard Blessed Be used as a sigh of relief before but other than that I have no other knowledge or any other usages. 
Anybody else know? 
if you do can you answer in the comments?