Email Deliverability.

Two terms are often confused. The delivery rate tells you how many emails were accepted by the receiving server, meaning they did not bounce. Deliverability goes further: where did the accepted email end up, in the inbox, in a promotions tab or in spam? An email can be delivered to 100 per cent of recipients and still be seen by nobody. For quotes, invoices or login codes that is just as frustrating as for a newsletter.

The technical foundation is authentication with SPF, DKIM and DMARC. It proves to the receiving server that the email really comes from your domain and was not altered on the way. Since February 2024, Google has required senders who send more than 5,000 messages a day to personal Gmail addresses to use all three methods, offer one-click unsubscribe and keep the spam complaint rate low (source: Google Help, 'Email sender guidelines'). For smaller senders, too, SPF and DKIM are now essential to arrive reliably.

The second part is the reputation that mailbox providers assign to a domain and a sending server. It drops when many emails go to invalid addresses, recipients mark emails as spam or volume suddenly jumps far above the usual level. It rises when recipients open, reply and rescue emails from spam. Clean lists are therefore crucial: sign-up with double opt-in, invalid addresses removed immediately, inactive recipients no longer emailed after a while. Purchased address lists damage your reputation and, in Switzerland, mass advertising without consent is generally prohibited under the Unfair Competition Act (UCA, SR 241, Art. 3 para. 1 let. o).

Content and structure play a part too, if less than often assumed. An email that is just one image without text, shortened links from unknown services or a sender that does not match the domain look suspicious. It is also important to separate types of email: transactional emails such as order confirmations should not suffer from the reputation of marketing emails. Many businesses therefore send them via a separate subdomain or service. The open rate is of limited use as an early warning because it is distorted; bounce and complaint rates and test sends to your own mailboxes at several providers are more reliable.