The spelling of "MMSUK" can be explained using the International Phonetic Alphabet (IPA). The pronunciation of this word is /ɛmɛmɛsjuːkeɪ/. The initial "M" represents the sound /ɛm/, followed by the repeated "M"s which represent the sound /ɛm/ as well. The letter "S" represents the sound /ɛs/, and "U" represents the sound /juː/. The final "K" represents the sound /keɪ/. Therefore, the correct way to spell "MMSUK" is with two "M"s and one "S" followed by "U" and "K".