How do you say i mailed him a lot of letters

Here are a few ways to express the idea "I mailed him a lot of letters":

1. I sent him a plethora of letters.
2. I bombarded him with letters.
3. I flooded him with mail.
4. I wrote him a multitude of letters.
5. I dispatched a large number of letters to him.
6. I showered him with correspondence.
7. I inundated him with letters.
8. I penned a large quantity of letters to him.
9. I dispatched a barrage of letters.
10. I wrote him a plethora of missives.

Note that some of these phrases may have slightly different connotations or nuances, so choose the one that best fits the context and tone you're aiming for.