Send HEY mail with forwarding address using Office365 SMTP

HEY mail announced a while back you can send emails from external email addresses using SMTP. Just the other day, they now finally also announced that their take on custom domains.

I’ve been waiting to hook up my existing HEY mail address with my custom domain’s forwarding addresses, so that I don’t have to set up MX records for email on my custom domain’s DNS.

In my case, I was hoping for something more similar to what GMail’s offering is like, where you can choose to send email from any other email addresses which you can receive email from (e.g. forwarding addresses, registered directly in your domain registrar’s DNS settings).

This guide outlines a solution I’ve found, which works great for me, where I can now finally send HEY email from a custom domain forward address, using the Office365 SMTP.

What you’ll need

Pros over setting up MX records on your DNS

Pros over HEY mail’s official custom domains feature


  1. In your domain registrar’s website, setup your desired email address <username> and forward it to your <username>
  2. In your Microsoft account, set up <username> as “Microsoft Account Alias”
  3. Once this has been done, verify that you can send email using <username>, from the web UI at
  4. In your Microsoft account, set up an “App password”.
  5. In HEY mail’s account settings, go to “Forwarding & SMTP setup” and add <username> Also add SMTP details, and use the ones from Office365 (you can find these details under the “Sync email” mail setting):
    • Outgoing (SMTP) server:
    • Port: 587
    • Username: <Microsoft username>
    • Password: <app password>

Now, when composing emails in HEY mail, you can choose whether to send the email as <username> or <username>!

Closing comments

All your emails are now stored in HEY, but you will also have all sent emails stored in Office365, where you have 5 GB of free space.