I have two accounts through webmail/roundcube. One of them I can receive emails on with no issues what so ever. The other account simply refuses to receive emails. They are not being blocked or marked as spam. I am not sure where to even start as to figuring out how to resolve this issue. Both accounts are set up the exact same.
Roundcube is a mail client so it has no role in receiving email. Have you checked your SMTP server logs?