'+' chars in the email content are encoded/received as as +. This is true regardless whether

• a '+' is included verbatim
• an email template is used
• any content containing a '+' is read in from file.

Use case: attempting to inline base64 as image source will cause image non-renderable, due to &#43.

Note that this also affects any data that is inlined by the email-ext plugin via the inline-data attribute on <img> tags (handled/processed by CssInliner).