There are different flavors of MOBI format. The older MOBI-7 format does not support font boldness. However a Master-MOBI (called MOBI-both in calibre) contains both the older MOBI-7 and the newer KF8 in a single file. That type of file can be emailed and synced and will allow font boldness.
I recommend creating Master-MOBI format using Amazon's Kindle Previewer software. MOBI-both files created using calibre sometimes fail to work properly when emailed.
|