In this case we write a letter to them as if they were going to receive it and keep it as a reminder of the gratitude we have for them.

如果情况不允许，那我们就写一封信给他们，就仿佛他们能收到它一样，然后保存这封信，时刻提醒自己我们十分感谢这些曾经帮助过我们的人。

youdao

Please consider this letter as a friendly reminder.

谨以此函向贵方做出友好的支付提醒。

youdao

I wrote this letter for you to keep, and when you need a reminder of how I feel.

我写这封信给你随时、当你需要提醒我的感受。

youdao

She plans to be there clutching Kennedy's letter, a reminder of those who paved the way for the long journey she is on the cusp of completing.

NPR: Obama Immigration Aide Seeks To Finish Journey