Here they are:
- Contact your pen pals - Tell them that you are very busy at the moment and that your letter may be slightly delayed. They really wont mind and it gives them peace of mind knowing you haven't just forgotten them.
- Prioritise - Yes keeping contact and writing letters regularly is important for keeping a good relation with your pen pal, but its not the be all and end all. Getting your exams right is the most important thing at the moment. Don't forget that after summer exams comes a long summer where you can write letters as frequently as you wish.
- Shorten your letters - If you really can't go without replying to your pen pals ASAP then just make your letters a little bit shorter. They will appreciate any letter long or short... Promise.
- Relax - Snail Mail shouldn't stress you out, after all it is just a bit of fun. Your exams will be over before you know it and then you can get back to long interesting letters.
I hope that helps! If you have any more tips add them in a comment :)