How would you design gift acknowledgements so that no donor is missed?

I treat it as a process with a measurable service level, not a mail-merge.

1. Use the platform's acknowledgement and tax receipt capability with document generation against the fundraising records, so the letter is produced from the data and the fact that it was produced is recorded.
2. Segment the treatment. A $20 online gift, a $10,000 major gift and a tribute gift that requires notifying a family are three different processes, and trying to serve them with one template produces bad letters for all three.
3. Define the service level explicitly — for example, acknowledged within three working days — and then report against it. That turns “did we thank everyone?” into a number someone owns.
4. Build the exception path deliberately: anonymous gifts, donors who have asked not to be contacted, gifts awaiting designation confirmation. The failure mode is almost always an unhandled exception queue nobody looks at.
5. The trade-off to be honest about: heavy personalisation looks better and scales worse. I would rather have a slightly generic letter that goes out reliably than a beautiful one that goes out in six weeks.