Most often when we are writing emails asking for a favor it’s nice to say how thankful you’d be or how you’d appreciate the help. In emails I often see phrases like: 

• I will be appreciated if you can reply.
• I’d be appreciated if you can let me know.

The above sentences don’t really make sense. They are incorrect expressions.

Yes, ‘appreciate’ is a verb here but with this verb it matters on ‘who’ is showing the ‘appreciation’.  If you use the subject ‘I’ then:

• I will appreciate. (‘I’ is showing the appreciation. “I am thankful.“)
• I will be appreciated. (‘Other people’ are showing the appreciation to ‘me’. “Others are thankful to me.")

This is why the example sentences are incorrect because it’s got the party showing the appreciation mixed up.

Therefore if you want to use ‘I’ as the subject, the correct expressions are:

• I will appreciate it if you can reply.
• I’d really appreciate it if you can let me know.

Note we need to have the object ‘it’ after ‘appreciate’

You can also use ‘it’ as the subject:

• It’d be appreciated if you can let me know.

However, it’s easier to write:

• It’d be great if you can let me know.

If you want to show your appreciation AFTER the favor has been done:

• I really appreciate what you’ve done for us.  (NOT I am really appreciated at what you have done.)
• I really appreciate that you’ve helped us.
• I am really grateful for your help. (‘Grateful’ = show appreciation of)

That’s all for today. Thanks for reading.