Polite Way of Saying "I can't...(answer the phone)" (しかねる vs. できない)


I'd like to ask about a polite way to say "I can't (do something for you)".
I'm sure the answer will depend on the context, so specifically, I'm curious
about how to convey "I won't be able to answer the phone from..." over email
in a business setting.

My attempt is:

海外旅行のため、1月10日から21日まで電話で対応しかねますので、大変ご迷惑をおかけしますが、メールでご連絡をお願い申し上げます。

My specific questions are:

  1. Is しかねる valid for politely giving this type of "excuse" for why you can't do something?
  2. Can できない also be used for politely giving this type of "excuse" for why you can't do something? (e.g., "電話で対応できませんが…")
  3. If neither of these are polite/appropriate in this case, what is a better alternative?




>   1. Is しかねる valid for politely giving this type of "excuse" for why you
> can't do something?
>

~~出来かねる or~~ 致しかねる is better. and I think, it's better not to mention about
the detailed reason.

>   2. Can できない also be used for politely giving this type of "excuse" for why
> you can't do something? (e.g., "電話で対応できませんが…")
>

Yes.

>   3. If neither of these are polite/appropriate in this case, what is a
> better alternative?
>

"1月10日から21日まで休暇を頂くため、お電話での対応を致しかねます。 ~~恐れいります~~
恐れ入りますが、ご入用の際には、メールにてご連絡下さいますよう、お願い申し上げます。"




>   1. Is しかねる valid for politely giving this type of "excuse" for why you
> can't do something?
>

~~出来かねる or~~ 致しかねる is better. and I think, it's better not to mention about
the detailed reason.

>   2. Can できない also be used for politely giving this type of "excuse" for why
> you can't do something? (e.g., "電話で対応できませんが…")
>

Yes.

>   3. If neither of these are polite/appropriate in this case, what is a
> better alternative?
>

"1月10日から21日まで休暇を頂くため、お電話での対応を致しかねます。 ~~恐れいります~~
恐れ入りますが、ご入用の際には、メールにてご連絡下さいますよう、お願い申し上げます。"

