〜ても差し支えない
it's all right to, you may (formal)
Verb て-form + も差し支えない / 差し支えありません · 差し支えなければ
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ても差し支えない is a very formal way of giving permission: 鉛筆で書いても差し支えありません, "you may write in pencil". 差し支え means "hindrance", so it's literally "there's no obstacle if you do".
It's the business and official equivalent of てもいい and ても構わない. You'll see it in instructions, forms and customer service.
As a question, ても差し支えないでしょうか is a very polite way to ask permission.
The set phrase 差し支えなければ means "if you don't mind", and softens a request for personal information: 差し支えなければ、ご住所を教えていただけますか. In both uses, the speaker is being careful not to impose, so the pattern suits emails, forms, offices and polite requests to strangers.
Examples
鉛筆で書いても差し支えありません。
You may write in pencil.
少し遅れても差し支えない。
It's fine to be a little late.
こちらの席を使っても差し支えないでしょうか。
Would it be all right if I used this seat?
お名前は書かなくても差し支えありません。
You don't need to write your name.
差し支えなければ、ご住所を教えていただけますか。
If you don't mind, could you give me your address?