This is a bit complicated and perhaps a low order problem and I'm a bit reluctnt to mention it but it is a mystery with 2 CLUES.
Here's a problem I've had for several years: Sent emails (emails I have sent) are recieved in a very tiny font. Maybe 4 pt.
Tried lots of settings in OEX and IE8 (and IE6 before that). Never have got it squared away. Have used OEX with Windows XP over the years both with and w/o SP 3. I've told recipients to paste the mssgs into a text editor if they can't enlarge the font in the as-recieved email.
Recipients use variously Macs and Windows some linux.
Altho I check and heavily filter incoming email on-line I do send 98% of outgoing email directly from my computer which must therefore be where the problem originates.
THAT MUST BE A CLUE!
I sent several emails to an Inbox account I have and got a tiny 4pt font when opening Inbox with Google Chrome, Iron Chrome and FF but opening Inbox with IE8 guv me the desired 10 pt type size; presumably because OEX is some dependent on IE.
THAT MUST ALSO BE A CLUE!
Mssgs I send to my Yahoo on-line account show up as 10 pt as desired. Email mssgs sent Yahoo to Inbox show up as 10 pt as desired.
When composing the mssgs I have OEX set for New Courier 10 pt but it shows up as about 14-16 pt in the composing pane where I'm typing. (It seems 10pt in OEX is not the same as 10pt in Wordpad. Arial 10 pt is not the same size as new courier 10 pt in word pad or OEX.)
Possible Clue? dunno.
Google searches haven't helped - yet - tho the problem does show up but mostly it seems the recipients believe the problem is on their end and not a function of the sender's machinery.