Plain text email uses base64 encoding

Moved from a Passport to a KEYone only to discover that outgoing plain text emails get rejected by the recipient. Checking showed that even though the Content-Type: text/plain the Content-Transfer-Encoding: base64. Surely it should use simple ASCII text?

Searching for a solution it seems that Android has been this way since 2010.

Is there a way to avoid the base64 encoding so that the email behaves the same way as BB10 and other common email clients?

This is probably an SMS (raw text) vs MMS issue. Open the Text app Advanced settings and try setting it to Use Simple Characters.