The presence of certain characters in the message, or the simple fear of the
potential presence of such characters in the message, causes mail programs
to turn on one of the two available mail encoding options, quoted-printable
and base64. The exact conditions that trigger this and the choice of one
method over the other depend entirely on which mail program you are using.
From your description, the Blackberry appears to always pick base64, but
perhaps it can be configured to use quoted-printable, which does not look
like garbage to recipients of the plain-text digest. As for what triggers
encoding on the Blackberry, who knows? Perhaps it saw an 8-bit character
somewhere in the original message, or in the address book, and it decided to
enable encoding just to be on the safe side. Some mail clients appear to
always use base64 encoding, without reason. The only solution is to use MIME
digests.

  Eric