Ideally record at high sample rates and bit-depth. For example: 88,2 khz and 24 or 32 bit float.
Please provide several version of your mix, e.g.: vocals +/- 1dB.
Sometimes mastering causes certain frequency ranges to stand out in the mix.
That way I can compensate for this fact. Your mix should have a headroom of -2 dB to -4dB before hitting digital zero.

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