If you would like to send invoices by email using the Billomat system, then it is crucial that you read this passage. If not, then feel free to skip over it.
If you visit Settings > Administraion > Mail server (SMTP/IMAP), there are a number of email settings open to configuration. The SMTP server is important for sending emails. Although you may certainly leave these fields open (meaning that emails are routed through our server), this is not to be recommended. While your own email address would be listed as the sender (email@example.com), the mail server billomat.net would actually be doing the sending. And, since yourcompany.com and billomat.net do not match, some spam filters might react aversely. So your safest bet is to enter the data of your own SMTP server. If you need help obtaining the correct data, contact your email provider.
IMAP, in turn, involves received mail. If your email service supports IMAP, then you can enter this data in the settings. Then, when Billomat sends an email for you, it will automatically also be saved in one of your email account folders. A good place would be the sent mail folder. Or you can create a special folder for emails sent via Billomat.