How do you handle order confirmation emails for backordered or out-of-stock items?

This is crucial. In my experience, the more information provided in the initial response as to exactly what component/piece/part is causing an issue and what is being done to resolve it, the more likely it is that another party will be able to effectively assist and resolving the issue or at the very least advocating for you. Also by providing a clear response, redundancy and over-communication is reduced, because the person receiving the answer is able to cascade clear expectations to management or other involved parties.

Be honest from the start. If you don't have it in stock say so. Give expected dates but make sure you explain its not exact unless you know for sure. Manage expectations. If possible offer a suitable alternative sometimes this may just be the answer and help complete a job. Even if you lose thus order the honesty is remembered.

This is probably one of the most common things that I end up having to come back with and ask suppliers or places I am ordering product from because they do not often provide a date upfront. Even if a specific date can not be provided, it is helpful is a response includes details on how long the production process is or turnaround process is once a shortage is received, how long transit time is from the location, or really anything that can be pieced together to produce a roughly estimated timeline. That rough timeline, even if too long or worst case scenario, is better than having nothing at all. Split shipments are willingly accepted in most cases because it keeps some traction on production lines, so it is positive for all parties.

This is another case where the process itself can be highlighted in conjunction with the features. For instance, a specific plating or galvanizing process may be adding additional time, but produces quantifiable, positive, long-term results. The same can be said for tier supply chain issues. If the issue is with a tier supplier and is delaying the order, try to emphasize why that supplier has been chosen to provide this specific part or component.

In my experience, discount codes and or store credits do lead to a repeat purchase despite the delays or current issues. This is for the simple fact that customers do see value in discounts or credits and do not want to feel as if they've wasted that, even if received to compensate for a poor experience. It also gives them opportunity to make another purchase with less or no perceived "risk," as they now are aware delays are possible and will choose something they want but with less sense of urgency surrounding it.

I agree but also make sure that your links do not take customers to a bot only, or, if they do, make sure there is a clear way to quickly transfer to a representative or other method of communication if the bot cannot quickly and efficiently resolve the issue. Many customers end up having a bot force them into typing their issue 5-10 different ways before allowing them the option to speak to an agent or get a phone number to call, etc.