The use of DKIM (DomainKeys Identified Mail) usually improves deliverability. DKIM and SPF (Sender Policy Framework) are the most applied methods to authenticate senders.
The establishment of DKIM for a sender domain provides a digital signature in the header of all emails that are sent with the sender's domain on promio.connect. With this signature the recipient can validate the identity of the sender by matching it with a public key and thus verify the authenticity of the email sender.
For promio.connect sender domains, setting up DKIM is mandatory.