Dear Mohammed,


I hope you and your family are all well? I haven’t seen you for such a long time, so (the comma replaces 'so' in this case) I must say that I really miss you.

I would like to remind you about the Red Road book which you borrowed from me last summer. I am sure that you enjoyed reading the story of the book because I know you're fond with of science fictions stories. This (that/the would make more sense) book has a sentimental value for me because it is  was (you could say 'is' but since you mentioned the time in the past when she gave it 'was' is more appropriate) a gift from my grandmother in for my 20th birthday. I was happy (you could maybe use a more interesting synonym like ecstatic or overjoyed) when I got it because I had wanted it for long time. As you know, my grandmother passed away six months ago and I would like collect all her souvenirs and put them at in a special place in the sitting room. Due to For this reason could you please bring it with you next holiday ?

I will be happy to see you soon.(looking forward to seeing you soon is a more natural way of saying that).Give my greetings to your sweet family.

Best Regards
Hassan Al
(Great! Pretty much grammatically perfect, just a few phrases that are unnatural in English)