Thank you for reaching out to the Constant Contact Community. It's my pleasure to assist you today.
I understand how important it is to receive your emails. Are the emails not hitting Outlook at all? Since you mentioned it seems to be intermittent, I would like to take a look at the individual emails. Can you send an email to social_support(at)constantcontact(dot)com with your username, the name of a few of the emails you have experienced the problem with and a referene to this post? We will be happy to investigate further.
Thank you for choosing Constant Contact. Have a good day!