March 10, 2021

Some notes on using HEY with Fastmail

(crossposted from HEY World)

So you’re interested in trying HEY, you’re a Fastmail user, and you want to forward some domains into HEY. Maybe you want to be able to send email from HEY using one of those domains. I’m that guy too and ran into a couple of issues so I’ll share here on my first post on HEY World. Just to be clear: this only applies to using Fastmail with HEY. It only applies when you are using Fastmail to control your domains for email.

When you set up your forwarding in HEY you need to set up forwarding for your actual Fastmail account (the one you login with, like into HEY. You don’t actually have to forward emails from that address but something in the way Fastmail forwards emails requires you to set up that address as a forwarding address inside of HEY.

If you want to send email as a different address from HEY it looks like you can make one choice of email address to use. That address needs to be the one set as the default sending identity in Fastmail. An example probably will make this clearer.

Lets say you have three domains set up in Fastmail with one address each:

And, lets say that your actual Fastmail login is

If you go into Fastmail’s settings there is an option for Sending Identities. That screen has a dropdown to select the default that will be used when you’re composing an email in the Fastmail web UI. More importantly to this discussion: it also controls the email address that a user will see when you send emails through the Fastmail SMTP server, as you do when you set up HEY to send email using another address.

So in this example we want to send email from HEY using and it’s been set up already on the HEY side with the proper SMTP setup. If you don’t select that address as the default in Sending Identities in Fastmail the email will show up at it’s destination as coming from and not This is the behavior I witnessed when sending to multiple different email services from HEY using one of my domains.

This certainly isn’t ideal behavior but it seems to be the limitation that anyone using the combination of Fastmail and HEY needs to live with until custom domain support is available in HEY in the coming months.

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