What are fallback font strategies?

You're using a custom font in your email, but you know it won't work in every client. So you need a backup plan. A font stack lists multiple fonts in order, and the email client uses whichever one it can find first. Your job is to start with your ideal choice, add similar alternatives, and end with a generic family that every system has.

Here's a real example: font-family: 'Proxima Nova', 'Helvetica Neue', Helvetica, Arial, sans-serif; This tells the client, 'Try Proxima Nova first. If that doesn't work, use Helvetica Neue. Then Helvetica. Then Arial. If none of those exist, use whatever sans-serif font the system has installed.'

Always end your stack with a generic family. These are your catch-all options. sans-serif means the system's default sans-serif font. serif means a Times-like font. monospace means a Courier-like font. This guarantees something will render instead of the client falling back to its own default (which might look terrible). Learn which fonts are web-safe and work everywhere, then understand why web fonts sometimes fail in email so your fallback strategy makes sense. Test your font stack across clients so you see exactly what your audience gets.