This occurs when the app is not unicode savvy or when text is corrupted on the way, in your case prob. in the Exchange server. I am not a specialist in how to set such devices to work, but you may test how things are or are not deformed by sending a test e-mail with contents like
ăĂ â îÎ șȘ țȚ şŞ ţŢ
áéěíóúůý ąǫę ȧė čďťřšťž ćśżźł ǧğ [Central European languages]
ασδφ ΆΈ ἀ ὡ ὠ ῠ ᾶ ῆ ά ᾱ ῑ ι ᾳ ῳ [Greek and Plytonic Greek]
ᴔ ᴙ ᴕ ᴉ ᴃ ᴝ ʚ ɷ ɘ ɼ ɽ ʉ ª [Phonetic transcriptions]
асдф ь ъ а́ е́ Ҧ ҙ ҏԙԏ ꙟмпэрат бг҃ е҃ аⷬ еⷮ [Cyrillic]
CDM: ā̱̣̆́ ḕ̱̯ ṃṇḷṛ ṝ̆ [CDM: combining diacritical marks]
If Unicode encoding is well preserved, you must send and receive the text EXACTLY as it should be.
P.S. After posting, it is correctly displayed in Safari so you may copy-paste it and make the test. Check also text encoding in your mai app. In Mail.app it is under Message/TextEncoding