0Outlook 2007 generating corruption in some sent e‑mails

I recently encountered a very strange prob­lem in out­look 2007. E‑mails sent to large num­bers of recip­i­ents (approx 30) were suf­fer­ing from some cor­rup­tion where a large part of the head­er was appear­ing in the con­tent of the e‑mail. The appeared as a long string of ran­dom char­ac­ters fol­lowed by some text (eg “Sosha1_v1;7” and “x‑cr-puzzleid”) that sug­ges­ted the garbled text was part of the out­look anti-spam “post­mark” fea­ture. The e‑mail mes­sage appeared as nor­mal below this cor­rupt text. Anoth­er symp­tom of the prob­lem was e‑mail fail­ing to send prop­erly the first time send/receive was clicked.

Set­ting up this users account on anoth­er com­puter with out­look 2007 did not pro­duce the same prob­lems, and the ori­gin­al PC had pre­vi­ously been restored to work­ing order by remov­ing all e‑mail accounts, com­pletely unin­stalling office, and rein­stalling. How­ever, soon after the prob­lem recurred!

After a lot of tri­al and error we even­tu­ally real­ised that this seems to be a bug (which is repro­du­cible) in Out­look 2007, and is caused by using plain text for e‑mails. Most e‑mails do not suf­fer from this prob­lem, but e‑mails sent to dis­tri­bu­tion groups are con­sist­ently cor­rup­ted. Switch­ing back to HTML e‑mail cures the problem.