Getting mail into Microsoft Outlook

[MadAsASnakeNana]

I use Microsoft Outlook as my main mail "thing." A recent important email did not arrive when expected, did some checking and found out it was sitting on my account in Yahoo BT mail. I never check this, preferring to use Outlook. Does anyone know why this should happen, that emails do not get through to Outlook and is there anything I can do to force this.
Many thanks.