For best results, the minimum format standard should be: 24 bit, un-mastered stereo interleaved, at the sample rate used throughout the recording and mixing process (44.1kHz is the lowest accepted sample-rate).
Specific exclusions: no mp3’s will be mastered, also please do not convert an mp3 to a wave as this will not result in recovery of the lost quality. Consider that if an mp3 is mastered as a wave it will most likely be converted to mp3 again by the consumer resulting in a second stage of audio degradation of sound quality. It is easy to detect when a poor quality mp3 is converted to wave as it obviously lacks important information particularly in the high-frequency spectrum. The mp3 is strictly a consumer format and has no place in the music-production process.
Recommendations: please do not apply the following processes to your mix on the final stereo buss: limiting, maximization, harmonic effects like inflation or excitement, stereo widening, psycho-acoustic bass enhancers. Minimal buss compression is acceptable if its essential to the character of the sound you’re looking for, not if it’s to get control of the mix. I will manage level, compression EQ and stereo-image on the chain here in the studio.

I believe in the benefits of specialization. As a specialist mastering engineer the best results I can achieve are usually achieved when I work with specialist mix engineers who aren’t in the habit of mixing into mix-corrupting stereo-buss processors like limiters or aggressive mix-buss compression. If you intend to send your mix to a mastering engineer it makes sense to deliver mixes that give him options…mixes with reasonable dynamic-range (crest-factor). If you give me high RMS mixes you’re likely to get back slightly EQ’d versions of the same because most of the opportunities to craft and shape the track in terms of stereo field, EQ and dynamics will have been sacrificed for control. That said, there are no rules and high RMS mixes do work in some rare cases where the producer/mix engineer has a really great approach in an excellent mixing environment. I will treat it on a case-by-case basis.

I am happy to provide mix-feedback and will – if I believe better outcomes are likely.