Sent icloud email reported as "malformed header"

Question

A friend found one of my icloud account emails in their spam folder, automatically put there by their email provider. In the message they had appended a scoring for why the email had been put there, some of which was based on the content I sent (mostly a picture), but also they noted that the header of the html email was malformed: "Bad headers on message from free email service". Has anyone else seen this and/or know of a solution to avoid emails I send (from Mail.app) getting marked as spam? Here was their report:
Content analysis details:   (2.2 points, 1.0 required)
pts rule name              description
-2.3 RCVD_IN_DNSWL_MED      RBL: Sender listed at http://www.dnswl.org/, medium
                            trust
                           [17.172.108.249 listed in list.dnswl.org]
0.0 FREEMAIL_FROM          Sender email is commonly abused enduser mail provider
                           (devans[at]mac.com)
-0.0 RCVD_IN_MSPIKE_H3      RBL: Good reputation (+3)
                           [17.172.108.249 listed in wl.mailspike.net]
0.7 HTML_IMAGE_ONLY_20     BODY: HTML: images with 1600-2000 bytes of words
0.8 HTML_IMAGE_RATIO_02    BODY: HTML has a low ratio of text to image area
0.0 HTML_MESSAGE           BODY: HTML included in message
0.0 URIBL_BLOCKED          ADMINISTRATOR NOTICE: The query to URIBL was blocked.
                           See
                           http://wiki.apache.org/spamassassin/DnsBlocklists#dnsbl-block
                            for more information.
                           [URIs: gwenbell.com]
-0.0 RCVD_IN_MSPIKE_WL      Mailspike good senders
3.0 MALFORMED_FREEMAIL     Bad headers on message from free email service
0.0 T_FILL_THIS_FORM_SHORT Fill in a short form with personal information

Answer 1

Yes, you understood correctly.  From your explanation, you created your hotmail.ca ID by revising the shaw.ca ID.  Given that, you should perform the steps listed in my original post:
Make sure you are signed into iMessage and FaceTime with your current ID.  If they are signed into the old ID, go to Settings>Messages>Send & Receive and Settings>FaceTime, tap the ID, sign out, then sign back in with your current ID.
Then temporarily recreate the old ID by going to https://appleid.apple.com, click Manage my Apple ID and sign in with your current iCloud ID.  Click edit next to the primary email account, change it back to your old email address and save the change.  (You should not have to verify the old email account so it doesn’t matter if you no longer have access to it.)  Now go to Settings>iCloud, turn off Find My iDevice and enter your current password when prompted (even though it prompts you for the password for your old ID).  Then save any photo stream photos that you wish to keep to your camera roll (unless using iCloud Photo Library).  When finished goThen go to Settings>iCloud, tap Sign Out (or Delete Account if you are not running iOS 8) and choose Delete from My iDevice when prompted (your iCloud data will still be in iCloud).  Next, go back to https://appleid.apple.com and change your primary email address back to the way it was.  Now you can go to Settings>iCloud and sign back in with your current iCloud ID and password (your data will download back to your device).