One of the most common reasons why e-mails do not reach the customer can be solved with an entry in the own Sender Policy Framework (SPF). This policy is meant to prevent the falsification of the sender address of an e-mail. The owner of the domain needs to specify which computers are allowed to send e-mails for this domain in the domain name system.
For example, if you use an e-mail with @mycompany.de as the sender address, the recipient's server (e.g. @gmail.com) checks whether the eTermin server is authorized to send an e-mail from @mycompany.de. Without an SPF record, the answer is generally "no," and that's a good thing.
For eTermin to be able to send e-mails using your domain, please specify the address of the eTermin mail server: 22.214.171.124. The updated spf record could look like this: "v=spf1 a mx ip4:126.96.36.199 -all".
An alternative to the SPF entries is the option of using your own e-mail server for sending. You can find out how this works here.
Another alternative would be to use the address email@example.com as the sender address. To set this up, you can simply leave the Sender e-mail address blank in the "Company > Settings" menu item under the "Communication" tab.
Notice: If you created a security rule that bans mail traffic from your domain through an external server please note that additionally to the spf record you need to add our IP-address, which is referenced to in the spf record, to the mail traffic rules of your Exchange-admin-centre.