We've recently discovered that email being sent with ASP Smart Mailer is increasingly being trapped by Spam filters, notably Postini (a Google product with increasing share).

This is a serious issue. The various best practice guides and spam check services point out that the emails composed with Smart Mailer fail in two ways:

1) MIME encoding should be multipart/alternative - emails should contain both a Plain Text Part and an HTML part - ASP Smart Mailer currently only encodes as "multipart/mixed". This is causing Postini and possibly Yahoo to trap our emails. The SpamAssassin flag associated with this is "MIME_HTML_ONLY". Refs: Wikipedia| SendBlaster

2) Base64 encoding unnecessary - according to a variety of online apps and software - base64 encoding is not required. Accordingly, it triggers a poor rating in the likes of the "FROM_EXCESS_BASE64" spam check field in SpamAssassin, Postini and others.

Would you please indicate how we can:

(a) include a plain text part in our HTML emails? (perhaps using a field maps to a plain text part), and

(b) modify the smartmailer.inc code (or page code) to produce an email encoding other than base64?

Your response would be appreciated greatly.

Regards,
Justin