MS Outlook 2010 not saving sent emails

Just returned from a weeks holiday and having sent a few emails this morning I see they arent saving in the sent folder.

I've checked the settings in Outlook and nothings changed - its set to save sent emails in the sent file.

Its really odd because I see them go to the sent file for a second or so and then they disappear.

Any suggestions much appreciated.

Monday is not going to be fun if I cant sort this out.

Many thanks