In Germany the law has been that you only need a DPO if a) you are a public authority, b) at least 10 people in your organization/company handle or have access to personal data or c) you handle sensitive data (e.g. health records).
As far as I know the GDPR doesn't change these requirements here. So even if you're a company of 5 people and just handling some email addresses or similar data you certainly don't need a DPO.
Under the GDPR, you must appoint a DPO if:
you are a public authority (except for courts acting in their judicial capacity); your core activities require large scale, regular and systematic monitoring of individuals (for example, online behaviour tracking); or your core activities consist of large scale processing of special categories of data or data relating to criminal convictions and offences.
So - no?