I check the content type of several e-mails. Some of them are in fact Base64, but many are of a differente type.
For example, I choosed just one, with this content:
-------------201E30CDCF21413A52EF849E
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: quoted-printable
In the Subject field in raw view:
Subject: =?UTF-8?Q?Re:_IIBB_Miguel_Ga=c3=b1an?=
When I try to find this message in "Main folder", I use the following options:
Text to search for: IIBB
Single phrase
Delete search result on exit (I have tried with and without this check mark)
Search the current folder only
No age or date constraints
It takes around 4 seconds to search, and comes back with no result.