Thank you for reaching out to the Community about your contacts. I'm sorry to hear you are unable to upload this email contact! Email address containing underscores in them should be allowed to be added in to your account. How were you adding this contact (typing in one contact, pasting or typing in multiple contacts, uploading a file of contacts)? Did you receiving any error messages? Has this happened in more than one browser or a private/incognito window? Knowing these details can help us try to troubleshoot this further for you.