During the past few weeks I've experienced twice that emails I've sent to users on hotmail.com don't arrive. Done some testing and found that if my sent message has no attachment, it arrives fine. If there is an attachment (pdf-file of 19kB) it doesn't arrive in the user's mailbox or in the junk mail folder.
The log from my mail server shows that sending went fine, and the message was transferred ok to hotmail's server. Message and attachment is virus checked before sending.
Anyone know what may be the reason for this?