1) "To whom it may concern" is typically used to address people that you are unaware of, and it implies a lot of distance. However, given that you seem to be addressing a specific volunteer organization, that addressee (though not known exactly) is pretty well defined, so I wouldn't use that phrase here. Actually, I would specifically say that the phrase makes sense to use if you don't care to ever hear back from the recipient. 2) "thought maybe I could become" - grammatically, this is perfectly fine, but in the context if a letter, it shows quite a low level of interest, so I provided some different phrasing. 3) "meaningful work related to" - grammatically fine, but a bit too impersonal. I suggested changes that focus more on your relationship with the work. Referring to your "eagerness" will imply this passion, in my opinion. :) 4) Reordered wording of the final paragraph to emphasize things differently (especially your desire to receive a reply). Good work, my friend!