Both of them had written so many letters for each other already since they first met on an online site. It wasn't something she'd normally do, to be honest. But she found it interesting, especially when she got to talk to him via chat and — as you guessed it — letters.
Handwritten letters. They both found it exciting to do it that way instead of the modernized and technological version of it. Regardless of the response time, the long wait would always feel worth it for both of them.
They would reply eagerly whenever one would arrive. And yes, they would both do it by hand.