I need to send an email to some clients telling them about my annual leave for holidays.
I would appreciate if you could give me any advice on how to improve this draft or help me correct any mistakes. Thanks!

Dear clients and friends,
Please be informed that I am going on my annual holidays from July 30 until August 8. I will be back to work and available for new projects on August 9.

I wish you a very happy summer,

Hi Laura

Welcome to EnglishForward.com

Your message is fine except I would say annual holiday (not annual holidays). If you have more than one holiday a year it isn't a annual holiday as by definition it is one holiday per year.
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Thanks, I really appreciate your answer. Is the "will" on the second sentence correct? I'm not sure whether it should be "going to".
Technically it should be going to as the plan was made before now, however I prefer will. I think it reads as more definate and avoids the repeatation of to.

You could say "I am returning to work on ------------------ and look forward to managing/handling your new projects." If you are concerned about will/going to future clauses.
I think this sentence improves the text very much.
Thanks once again for your help.
Have a nice day!
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You're welcome. Have a good day yourself.