@paok1970,
Quote:Do you find the use of "could" not "appropriate" (I don't know if it is the right word to use here) in the Longman example above?
'appropriate' is fine.
Context is everything in determining what language we use, Paok. This is the same for all languages.
The example sentence is fine, appropriate, fitting, dandy, alright, polite, ... .
'could' simply means, "if it is possible for you to ... ".
'most' added to grateful helps even more, as does "in due course".
Context is everything.
Make up some example sentences of your own. Then when you get some feedback that may help you a lot!