I have not had this problem until an incoming mail was too faint/light to read in its native font. I pressed Menu while reading it, selected "get plain text" and lo and behold, it bolded it up and was legible... (the sender used a yahoo acct)

however.... my reply was received by recipient in giant text, as was my bcc to myself, and any further replies to that thread all appeared to be in normal text from the sender side, but the recipient got it in giant text.

Reading the same emails retained on my laptop, everything was in normal font.

jan