Details
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Bug
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Status: Closed
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Major
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Resolution: Fixed
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1.1
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None
Description
Previous bugs (e.g. http://issues.apache.org/jira/browse/EMAIL-50 ) raised against commons-email version 1.0 have complained about Outlook not being able to properly display multipart emails generated by HtmlEmail. While this issue is resolved as of rev 510708, I believe there a several issues regarding MIME layout, that still cause trouble to email clients.
In the current codebase, a multipart email containing: plaintext part, html part, inline images and attachments, is constructed (to the best of my knowledge) with a MIME layout like this:
Generated by HtmlEmail. Contains parts: plaintext, html, embedded inline img, attach
PART#, MIME_TYPE, (COMMENTS)
1 multipart/related
1.1 multipart/alternative
1.1.1 text/plain (the plaintext content)
1.1.2 text/html (the html content with cid: references to embedded images)
1.2+ / (attachment)
1.3+ image/* (embedded image, referenced by 1.1.2)
("+" above indicates that multiple (1..n) parts may be included)
The above structure may cause email clients to display embedded images as attachments, even though they are semantically part of the text/html content.
Furthermore, the current codebase (as documented in the HtmlEmail.setMsg() JavaDoc) synthesizes a html part by <pre>...</pre> wrapping the plaintext part, thus generating a bloated (double size) message, for no apparent reason. In my opinion, HtmlEmail should degrade to the mime layout of Email, if no html part is available.
Proposed MIME layout
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To the best of my knowledge, a multipart email containing: plaintext part, html part, inline images and attachments, should be constructed like so:
PART#, MIME_TYPE, (COMMENTS)
1. multipart/mixed
1.1 multipart/related
1.1.1 multipart/alternative
1.1.1.1 text/plain (the plaintext content)
1.1.1.2 text/html (the HTML content with cid: references to embedded images)
1.1.2+ image/* (embedded image, referenced by 1.1.1.2)
1.2+ / (attachment)
The following simplifications of the above structure may be applied:
a. If no embedded images are included, items 1.1.2+ and 1.1 are removed.
b. if no text/html part is included, items 1.1.1.2 and 1.1.1 are removed
c. if no attachments are included, items 1.2+ and 1 are removed
Incidentially, this MIME layout is used by GMail, which is an indication that it is the "proper" way.
I seriously believe that this issue should be investigated and resolved, if at all possible, as part of version 1.1.
I may be able to supply a patch to HtmlEmail.java in the April/May 2007 timeframe, but I am not prepared to put any body parts on the block on that one 
I welcome any comments!
Morten Hattesen
References:
See http://en.wikipedia.org/wiki/MIME for additional information and references