Which emails the app sends and what to do about them

The app sends only the mails listed here. It sends no reminder before a due date, no mail for recurring invoices, payslips, month-end reports or approvals. Mails to you are sent automatically and say not to reply; the sender shows as accounting-ai. Mails to your customers and suppliers carry your company as the sender, and replies go to the client's contact email in the settings.
Sign-in code and invitation: the sign-in code mail has a code that is valid for the few minutes it names and works once; if you did not ask for it, ignore it. The invitation mail (Accept invitation) comes when an owner or admin invites you, with the date until which it is valid. Without an invitation the sign-in page says There is no invitation for this email address. If an invitation mail could not be delivered, the inviter sees a notice and has to withdraw the invitation and invite again later. If a mail does not arrive, look in the spam folder first.
Security alerts go to every owner of the firm or of the client, with only the last four digits of the account: Invoice IBAN changed (the IBAN printed on invoices), Supplier IBAN changed (an IBAN on a contact) and Contact IBANs imported (a migration stored IBANs on contacts). If nobody expected the change, check the settings or the contact now. Payment files use a new supplier IBAN only once someone picks it.
Period re-opened goes to the tax advisors of the firm or client and to whoever locked the month, but only when that lock was a tax advisor's sign-off or a DATEV export, and never to the person who re-opened it. It means the month they attested or exported is open again, with the reason the re-opener typed; the advisor should check it again before the next filing.
Mail to your customer: an owner or admin sends an invoice, quote, order confirmation, delivery note, cancellation or corrective invoice from the document with Send by email. It goes to the contact's invoice address and the CC and BCC you typed, with the PDF (and the XML of an e-invoice) attached, and the mail ends with your company details. A dunning letter is mailed when an owner or admin sends it, with the PDF attached and the request to ignore the letter if the invoice was already paid. Without an email address on the contact the dunning letter is stored but not mailed; the dunning list says Not mailed.
Mail to a supplier: the agent can draft a German letter asking for a missing invoice; the app never sends it, you copy it and send it yourself. For a received e-invoice that failed its checks, Request correction on the document opens a mail you send from the app: choose the Recipient from the stored addresses, add a note, choose Send email and confirm. Owner, admin, accountant and bookkeeper may do this. There is one request per document every 24 hours and at most 20 per client per day, and you can pick German or English.
When a customer mail fails, read the status in the list under the send form: Waiting to send, Sending, Sent, Failed or Undeliverable, with the reason. The send was interrupted; it is unclear whether the email arrived. Please check before sending again. means you should ask the customer before you send once more.