As the title suggests, I've got an issue where outlook 2007 is reporting it failed to send email with error 800ccc0f (unexpectedly terminated connection) but only with attachments.

The email is actually sent, but outlook keeps retrying (stays in the outbox), generating more emails to the original recipient (which do get delivered)

I've got QMail on the server side supporting a half dozen domains.

It doesn't appear to matter which account I send from. I can successfully send attachments via alternate mail clients (webmail, thunderbird) while outlook is failing, or send messages without attachments; so it's seemingly not the accounts themselves or serverside, which leaves outlook as the culprit.

There doesn't appear to be any pattern to the failures, and it's not consistent (I successfully sent an attachment as recently as 3 weeks ago) so I'm at a loss as to where to look. Qmail logs don't look any different between successes and failures.

Has anybody seen this before/have a solution?

UPDATE : It appears it's only PDF files that this occurs with, so I'm even more stumped. I can send html/docx/txt and zip, UNLESS the zip file contains a pdf ... whiskey tango foxtrot