Tell HN: Fastmail may be routing Calendar reminders via your work SMTP server

[gphilip]

I have set up Fastmail to read (IMAP over SSL) and send (SMTP over SSL) work emails. Over the last couple of weeks my Fastmail Calendar reminder emails started turning up in my Fastmail inbox as attachments to "Undelivered Mail Returned to Sender" instead of their usual avatar as "Reminder: Do XYZ" emails.

On raising a support ticket over this issue I learnt that Fastmail uses my work SMTP server to send these reminders (to my Fastmail email address!). I checked some recent reminders, and indeed, they have my work email address as the "From:" address, and they have been sent via my work SMTP server.

That is: Fastmail Calendar logs in to my work SMTP server as the "work me", whenever it wants to send me a reminder to my Fastmail email address.

If you have been---like me---working under the assumption that your personal Fastmail Calendar and your work email don't mix, it may be time to update that mental model. All your Calendar reminders may have been first sent to your workplace, before they come to you.

[akerl_]

I think I’m missing something. It sounds like you configured Fastmail to send via your work SMTP server, and then it did that. And this was surprising?

[gphilip]

I configured Fastmail to send emails that I compose from my work address, via the work SMTP server. Not any other type of email. And indeed, they don't send emails that I compose from my non-work addresses via my work SMTP server: they use their own server to send these.

The support person who is dealing with this also turned up the fact that this is a change that they made some time in 2019. Earlier to that, all emails from Fastmail Calendar were sent from the "[e-mail]" address. They changed this in late 2019 so that Calendar now sends these mails from my work address (following some peculiar logic and email rewrite rules).

So yes, it is surprising that they send emails from my Calendar via my work SMTP server.